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Our protagonist, Rimuru: slime... and human. note 
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After dying while protecting his junior colleague at work from a knife attack, Satoru Mikami is reincarnated as a slime in a magical world. As someone who is reincarnated, he gains the Skills "Predator" and "Great Sage". While strolling around, he meets the Storm Dragon Veldora who becomes his friend and names him Rimuru. In return, Rimuru gives the surname Tempest to both of them and agrees to snatch Veldora from his prison so that one day they can permanently break Veldora's prison. The mysterious disappearance of the Storm Dragon results in huge consequences as his presence acted as a sort of buffer zone. Meanwhile, Rimuru starts his adventure by traveling, meeting new people, fighting some of them, and turning them into allies by fighting them. He is guided by a mysterious interface, the Great Sage, which teaches him how to use his unique skill, "Predator", an almost limitless ability to eat and assimilate living things and objects. Rimuru begins to adopt the forms and abilities of everything he absorbs, which makes him very strong, but also a target.

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That Time I Got Reincarnated as a Slime (Tensei Shitara Slime Datta Ken) is a series of web-novels turned light novels by Fuse and illustration by Mitz Vah. This series is adapted to manga by Taiki Kawakami and an anime by Studio 8 bit. On September 21, 2021, following the conclusion of Season 2, a movie was announced for release Fall 2022.

It also spawned Spin-Off Manga including:

  • The Ways of Strolling in the Demon Country/How the Monster Country Works/A Travel Guide to the Land of Monsters (転生したらスライムだった件~魔物の国の歩き方~ Tensei Shitara Slime Datta Ken: Mamono no Kuni no Arukikata) (2016-): A series about Rabbit Girl Flamia exploring Rimuru's country and takes place further in the story.
  • The Slime Diaries: That Time I Got Reincarnated as a Slime/The Slime Diaries/Reincarnated Slime Diary (転スラ日記 転生したらスライムだった件 Tensura Nikki Tensei Shitara Slime Datta Ken) (2018-): A 4-Koma about Rimuru and friends (and sometimes villains) in their daily lives. An anime adaptation aired from April to June 2021, in the interim between part 1 and part 2 of the main anime's second season.
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  • That Time I Got Reincarnated as a Corporate Slave (転生しても社畜だった件 Tensei Shite mo Shachiku Datta Ken) (2018-): A series about Rimuru reawakening in the real world in a salaryman job similar to his previous life as Mikami, but still in his slime body.
  • That Time I Got Reincarnated as a Slime Another Story: Trinity of the Magic Kingdom (転生したらスライムだった件 異聞 ~魔国暮らしのトリニティ~ Tensei shitara Slime datta Ken Ibun: Makuni Kurashi no Trinity) (2019-)
  • That Time I Got Reincarnated as Kosaku Shima (転生したら島耕作だった件 Tensei Shitara Shima Kōsaku Datta Ken): A crossover where Mikami awakens as 37-year old businessman Kosaku Shima instead of a slime.
  • (転ちゅら! 転生したらスライムだった件 Tenchura! Tensei Shitara Slime Datta Ken) (2019): A 4-Koma about Rimuru where turns into a three-year old body after obtaining a human body rather then an adult.

A 2D turn-based role-playing and city-building game called That Time I Got Reincarnated as a Slime: Lord of Tempest (Tensei Shitara Slime Datta Ken ~Makoku Renpou Souseiki~) was released for iOS and Android. A 3D battle role-playing and city-building game called That Time I Got Reincarnated as a Slime: ISEKAI Memories (Tensei Shitara Slime Datta Ken: Maō to Ryū no Kenkoku-tan) was released for iOS and Android on October 28, 2021, introducing two original characters by the names of Shinsha (a slime who self-proclaims herself as Rimuru's daughter) and Izis (a mysterious Witch of Mirrors who can summon alternate versions of Slime characters).

There was also a crossover event for Last Cloudia.


That Time I Got Reincarnated as a Slime provides examples of the following:

  • Actor Allusion: This isn't the first time Tia Ballard voiced a pink-haired oni girl with two horns on her head.
  • Adaptational Attractiveness: Zig Zagged a bit with the "Slime Diaries" spinoff. As a whole, all of the characters receive rounder, cuter designs that make even the roughest-looking among them (like Geld) outright cuddly, but any of the normally hot and sexy characters (like Shion and Benimaru) trade the attractiveness for enhanced cuteness due to this art-style change.
  • Adaptational Personality Change: Several characters received notable changes to their personalities between versions (web novel, light novel, manga, and anime), as noted in each of their character entries.
  • Adaptation Distillation: The anime cuts out some of the side character arcs and compresses other things for the sake of pacing while still keeping some of the manga's expansions (Such as Shizu's backstory). For example, the "Adventurer's Arc" (a minor arc which shows how Rimuru got his Adventurer's License, sheds some spotlight on how the Adventure Guild works, and gives Elen, Kabal, and Gido some additional expansion and screentime) isn't covered by the anime specifically, but rather gets shown in the first Opening of Season 2, showing Rimuru about to head out with the three adventurers, as well as his "examination" fighting a set of monsters to boost his Rank from F to B with each "set" ending about as quickly in the fast-paced animation as they did in the light novel and manga.
  • Adaptation Expansion:
    • The light novel is fairly bare bones in presentation. For example, the character of Shizue has no speaking lines apart from asking to join the adventurers before succumbing to possession, nor does she actually do anything like torch giant ants to show off her strength. She just joins the party, is silent until meeting Rimuru, gets possessed, beaten and then dies while wishing for him to get revenge on Leon Cromwell for her.
    • While the Rapid-Fire Comedy nature of a yonkoma comedy is still present, the anime adaptation of The Slime Diaries heavily expands on all of the gags, taking what were four-panel quick jokes and turning them into full-blown scenarios that last at least a minute each.
  • Adventure Guild: The Free Guild, founded within Ingracia by the Otherworlder Yuuki Kagurazaka, functions as this. Notably, he reworked the original adventurer society into an internationally-accepted organization that helps fight monsters and better provides quality of life for humans. The irony being that he's actually the Big Bad, though in the light novel he's legitimate in having them do good. In the web novel they were meant to hold up his Villain with Good Publicity angle.
  • Alphabetical Theme Naming: When naming the goblins, Rimuru just goes through the Japanese syllabary in order, with "gob" in front: Gobta, Gobte, Gobtsu, etc.
  • Anatomy of the Soul: Souls are divided into three parts. The astral body that connects it with the physical body, a core that builds a protective shell and finally, inside the core, the nucleic Heart where the ego of a person dwells.
  • Anti-Magic: Certain spells and weapons are designed to be capable of bypassing or even negating magicules, which can not only disable Elemental/Aspectual Magics, but also inflict noticeable harm or at least act as a Power Nullifier on monsters since they're Made of Magic. However, contrary to what many humans think, this isn't absolute. In addition to just being so much stronger than the anti-magic to not be affected, several types of magic outright bypass regular anti-magic because their rules work differently. Spiritual Magic, for example, relies on a contract with and utilizing the powers of an Elemental Spirit, whose powers are based solely in natural phenomena rather than unnaturally affected by magicules, and so it can't be affected by regular anti-magic.
  • The Armies of Heaven: The angels are the personal armies of Veldanava that fight to protect the world from interdimensional invasions. And then Veldanava died because of the world's mortal races and the angels continued that duty while also nursing a deep grudge against them, which manifested in descending every 500 years to launch attacks on advanced civilizations to uphold Medieval Stasis. They then descend into full-on Omnicidal Maniac territory with the prompting of the Big Bad's Mind Control.
  • Armour Is Useless: Some characters wear armour, others don't, and it rarely makes any difference. A special mention goes to a scene in the anime version where a lizardman warrior kills an armoured orc by slashing his speartip across the latter's fully armoured back. Downplayed somewhat as high quality armor is anything but useless, and Tempest's entire army is outfitted with armour designed for their species, so it has some effectiveness at lower ranks.
  • Artifact Name: The otherwise Non-Indicative Name given to every non-demon "Demon Lord" originated with Guy Crimson, as the first independent demon to achieve his level of power. When creatures of similar strength started to appear, the name became a catch-all term, as each of them grew to be just as feared.
  • Asskicking Equals Authority:
    • In contrast to how humans and human-like races (dwarves and elves) maintain their rulership based on their capacity to lead regardless of personal power (there are strong human, dwarf, and elf leaders, but their power is secondary to how well they command their nations), completely inhuman races like monsters and demons maintain hierarchies based on who is the strongest. The absolute rulers of each non-human-based nation are the absolute strongest among them, along with all secondary leaders underneath them being leagues stronger than the regular soldiers. As a result of this power hierarchy, the idea of Royals Who Actually Do Something and Frontline Generals is present everywhere. Additionally, inhuman biology also incorporates Authority Equals Asskicking, as gaining a higher position in a hierarchy boosts a monster's abilities to make them better asskickers, with more asskicking-gained authority granting higher amounts of authority-gained asskicking power.
    • Up to Eleven in demon society as a whole. As demons are spiritual beings by nature who constantly fight each other in Hell, death leads to reincarnation, but in turn this shaves off some of their magicule supply with each resurrection. Enough losses in a row without recovery will actually result in a demon devolving, and once a demon hits Archdemon, they hit their natural "cap" and must rely on knowledge, experience, and cunning to hold their own. According to Diablo, the only way to reach the next stage of Demon Peer is to ass-kick your way to Archdemon, then maintain an undefeated chain of victories (or at bare minimum avoiding death and resurrection) for at least 2,000 years. It's notable that among confirmed Demon Peers, the only other ones aside from the Primordials are Veyron and Moss, who achieved unbroken win streaks for 4,000 years and 10,000 years respectively.
    • While it's technically a human-dominated nation, the Eastern Empire holds this ideal for their military, complete with official and organized methods of Challenging the Chief to rapidly advance in the ranks. The commanders of the three main divisions of the army are expected to be capable of defeating literally everyone else under them in said division. They also have no issue employing Otherworlders or even certain monsters into their ranks and giving them command positions if they're strong enough; the strongest member of the fourth "division"/Praetorian Guard and head of Empire intelligence is the former while the actual Marshall who is the Command-in-Chief is the latter.
  • Author Appeal: The author very clearly has a thing for cute monster girls, including Bizarre Sexual Dimorphism with dragonewts and eventually including hot demon girls.
  • Awakening the Sleeping Giant: Averting this is a big reason why foreign nations are willing to make deals with Tempest, a nation of monsters. A nation of over ten-thousand named monsters acting in unison could rain hell on any nation dumb enough to punch first. Falmuth and the Eastern Empire learned this the hard way.
    Hakurou: Our ruler is making his way towards that very battlefield. You people have gone too far. You angered the one person whose rage you should fear the most. You have my sympathy. Your death will not be painless.
  • Awesome, but Impractical: Several of the "test phase" weapons and armor Kurobee and his apprentices craft fall under this, mostly due to lacking Required Secondary Powers.
    • One suit of mail sucks at the wearer's magical force to erect a continuous and powerful magic barrier...but drains the magic power whether the wearer wants it to or not, eventually killing them from the drain. It has a corresponding sword that has a Life Drain effect...but also includes the user. The forger actually almost died during the creation process. Rimuru ends up giving them to Albert, as since he's The Undead he has no life force to drain.
    • A sword that attracts all magicules in the local area like a magnet and transforms them into explosive force. Great for making it impossible to cast any spells while providing a devastating attack...but it provides no protection whatsoever for the wielder itself from the explosions.
    • A suit of armor that grants the user extraordinary physical strength for a limited time. Amazing, but once that time expires, the wearer's muscles all rupture, leaving them motionless and dead unless they or someone nearby has healing magic on hand.
  • Awesomeness Is a Force: Downplayed with King Dwargo who is described by Rimuru as 'exuding an aura of raw power'.
  • Back from the Brink: Aptly described in Episode 47, "Returning from the Brink", with the twist being that it's Clayman who does so after spending most of the previous and this episode getting utterly humiliated both in the physical and mental sense as he finally achieves his Awakening, putting almost everyone at Walpurgis on edge...except Rimuru, for whom this was All According to Plan as the two prepare to face off.
    Clayman: The heavens haven't forsaken me yet!
  • Back from the Dead: Resurrection magic does exist, but it's a complicated art. The long and short of it is that no matter what it needs to be done as soon as possible because the soul starts to vanish and/or degrade upon death in most cases. If one doesn't do so, best case scenario is that it just fails. The worst case scenario is when you get something like what happened with Milim and the Chaos Dragon.
    • Normally, the holy spell/art Resurrection is one of the most powerful and difficult magics to master, and it needs to be cast as soon as possible on the deceased in order to preserve their soul. It also won't work if the soul is no longer present.
    • Ruminas Valentine's Unique Skill Lust and later Ultimate Skill Lustful King Asmodeus has resurrection as part of the package. It's much easier to revive even multiple people from the dead, but again the souls must be present which means timing is key.
    • The victims of Tempest who were slaughtered by the Kingdom of Farmus had their souls contained by the barriers around the city as a side-effect with Shuna and Myulan working to keep them in after they were dropped, meaning Rimuru had time to properly revive them before it was too late. He had to become a Demon Lord to even be strong and skilled enough with magicule control in order to properly revive everyone in the first place.
    • This goes up to Death Is Cheap levels within the Tempest Labyrinth. As long as you're wearing the Resurrection Bracelets crafted specifically for the dungeon by Ramiris, it doesn't matter how brutally you die in there since your soul will be preserved and your body will be brought back even free of all fatal injuries.
    • During the war with the Empire, Rimuru harvests the souls of the nearly million fallen enemy soldiers and revives 700,000 of them while having enough spiritual energy left over equivalent to a million harvested human souls. This is because many of the Empire's soldiers were artificially augumented to have souls equal to dozens to hundreds or even thousands of normal human souls. Reviving them in a reduced state thus left so much spiritual energy behind for his own use.
  • Bait-and-Switch: Shizu is introduced as Rimuru's major love interest. Instead, she becomes possessed and dies two episodes later, with her Dying Request being that he assimilate her and fulfill her last missions. Doing the former allows Rimuru to take on human form once again.
  • Balance of Power: Before Rimuru showed up, a rather complicated one exists throughout the world.
    • At its most basic level, there are three major powers: The humans, the Demon Lords, and the angels. The former two are the Type A and B powers, while the angels are the Type E who are out to kill anyone who develops technology too high. Luckily, the angels don't otherwise interfere outside of their 500-year scheduled purges, but whenever they show up things tend to devolve into a chaotic free-for-all.
    • Humanity is technically split up among themselves in its own balance.
      • With the Eastern Empire led by Emperor Rudra being the dominant force on their side, with the largest army, the most advanced human military technology, and the largest collection of the strongest humans alive. He technically has a Type E power in the form of True Dragon Velgrynd (who's probably as dangerous as almost the entire military put together), and he seeks to force the rest of humanity under the Empire's banner in order to destroy the Demon Lords and especially Guy Crimson, the strongest Demon Lord. Only geographical location, difficult logistics for a mass invasion, and the presence of other Demon Lords between the territories have prevented them from assimilating the western human nations under their banner.
      • The Council of the West is made up of The Federation of most of the western human nations. They have a Type C relationship with the Dwarven Kingdom of Dwargo, the Sorcerous Dynasty of Sarion, and the Holy Empire of Ruberios, who are all nominally aligned with the Council against the threat of monsters, Demon Lords, and the Empire, but all individually are of such independent self-sufficient strength they could ignore and go it alone if they wanted to. Plus, it's only known to few that the Holy Empire's "God" Luminous is actually the True Demon Lord Ruminas Valentine and its emperor is in fact one of her most powerful vampire servants, but their interests align in keeping humanity safe.
    • The Demon Lords are technically a loose alliance who go about their own business and have various stronger alliances between each other and some of them even have relations with the human kingdoms. Guy can be considered "leader" by virtue of being one of the strongest who can push around almost any of the others and come down on serious in-fighting, and he has his own True Dragon Type E power in the form of Velzard on his side while outright calling the other Demon Lords his "pawns" in his long game against Rudra. The only major rival he has in this regard is Milim Nava, and she barely has any interest in "ruling" and just does what she wants. This of course doesn't stop the others from scheming together to gain more power and possibly knocking off some of their fellows, such as Clayman wanting to ultimately off Leon Cromwell as revenge for his master Kazaream.
    • This balance then pretty much breaks once Rimuru comes on the scene and befriends True Dragon Veldora. His actions result in Veldora's disappearance from the Jura Forest (originally a free zone under his sealed protection smack dab between the Empire and the Council along with near several Demon Lord territories) and multiple factions trying to take it over. Rimuru ends up gaining power and followers before being declared administrator of the Forest by the dyrads for defeating a prospective Demon Lord; starts introducing massive cultural and technological reforms that turn his nation of Tempest into a powerhouse; eventually becomes a Demon Lord after crippling the human Kingdom of Falmuth's military and killing the manipulator Clayman, resulting in a full shift in the Demon Lords ranks; earns the respect and alliance of the Holy Empire, Council, Dwargo, Sarion, and Milim Nava; and amasses a large army of incredibly powerful monsters, including Veldora, the legendary Sword Saint and four of the Seven Primordial Demons (the other three being Guy and two of his strongest servants). By this point, Guy outright calls Rimuru a disruption of the balance between himself and Rudra. And then Rimuru actually fights the Empire and wins.
  • Beast Man: Several species and varying degrees of anthropomorphism from this to Little Bit Beastly.
  • Be Careful What You Wish For:
    • The world takes into account the target of the reincarnation's wishes before sending them along. Rimuru's casual and unknowing responses turn him into a slime.
    • Gelmud wants Geld to eat enough monsters so he can evolve into a Demon Lord. Geld proceeds to follow his orders exactly, starting by killing and eating his benefactor. This kickstarts his evolution, just like he wanted.
    • Twicefold for Shogou. He tried to goad Geld II into droping his arms (hoping for an advantage), only for Geld to not fall for his provocations. Later, as he's losing, he kills an ally in order to gain the skill [Survivor], which gives him regeneration and improved defenses, and claims that with it he's now invincible. This pisses off Geld enough that he decides to drop his weapons to deal out a No-Holds-Barred Beatdown. Thus, he learns the hard way that his improved defenses don't give him Pain Nullification and his regeneration only prolongs his suffering.
  • Bishounen Line: How power levels are gauged. When a monster is named, it becomes closer to looking human, while keeping previous traits. This means Rimuru, Treyni, Demon Pillars and other extremely powerful monsters appear as beautiful humans. Veldora subverts this, still looking like a dragon despite how powerful he is and when he actually gains a human form, it's more for convenience than an actual power boost.
  • Bloodless Carnage: Not normally, but it is actually more terrifying when there is no blood involved as the soldiers of Falmuth can no longer attest to.
  • Bland-Name Product: Before Rimuru dies at the start of the series, he tells his friend to destroy his hard drive. In an anime only end of episode gag we actually get to see him do this, and Rimuru's computer runs on "Mechasoft Doors".
  • Bookends: Episode 37 (the first episode of Season 2 Part 2) starts with Laplace running away from the Holy Church of Luminous at night after trying to sneak inside and being attacked and seemingly killed by Roy Valentine, only to mysteriously appear fine afterwards. Episode 48 (the last episode of Season 2) ends with Laplace once again running into Roy while trying to escape the Holy Church at night after failing to infiltrate, but this time he fights Roy and utterly dominates him before revealing he mysteriously managed to yank out Roy's heart during the beatdown right before finishing him off.
  • Breather Episode: The Slime Diaries, a lighthearted Yonkoma spinoff, aired its anime adaptation in the middle of the second season, right after the Famulth Kingdom's attempted invasion and Rimuru's subsequent awakening into a True Demon Lord and right before the Walpurgis Banquet where Rimuru and Clayman finally clash.
  • Bring My Brown Pants: Outside the Dwarven kingdom, when Rimuru scares a party of human adventurers off, he is informed that a portion of witnesses soiled themselves in the process.
  • Civilization Destroyer: The higher-level True Demon Lords, Primordial Demons and the True Dragons are all capable of this, with it being on record they destroyed plenty of countries and cultures in the past. The angels meanwhile carry out systematic purges of civilizations they deem as too advanced from their preferred Medieval Stasis. The only reason most don't get around to destroying the whole planet is either because they like the planet itself or they're stopped by the ones that don't want the planet to become a smoking crater.
  • Cannot Tell a Lie: Monsters are incapable of lying directly. If they lie, they'll disappear immediately. Lesser ones that are capable of normal sexual reproduction aren't held to this, however. However, when humans get too complacent about trusting monsters they tend to get tricked and screwed over badly: They're still capable of lies by omission or misleading truths. After awhile this idea is seemingly scrapped with the acknowledgement that monsters with a primarily spiritual body can also lie consequence free. So who exactly is bound by this rule?
  • Cardboard Prison: When briefly put in prison for (accidentally) causing a very large public disturbance outside the Dwarf city, Rimuru is put inside a barrel as well as a cell. As slimes in this universe are typically seen as one of the weaker beings and might be able to contain them, Rimuru is no ordinary slime. He gets out of it (and the cell) as soon as he wants to.
  • Characterization Marches On
    • In the web novel, Hinata Sakaguchi is introduced as a high-functioning sociopath who had already murdered her father to collect on his insurance money (though he probably deserved it considering he was a wife-beater and gambling addict who put the family in debt in the first place) and was considering murdering her mother soon for being a burden. When attacked after being summoned, she brutally murdered her assailants, though once again they weren't exactly sympathetic characters. However, by the time she comes into conflict with Rimuru, she's instead characterized as a slightly odd girl who is only trying her best to save people from dangerous monsters and has a habit of letting herself get led astray by her emotions. In subsequent adaptations, it's slightly altered so that her sociopathy is missing (though it still treats her killing her father and her three assailants as justified or at least understandable given circumstances) and her thoughts about killing her mother were brought from her descending into madness and a cult, with her personality pretty much consistent up to when she encounters Rimuru.
    • In the web novel, when Leon Cromwell has his first fight, it's made clear that when cutting loose he doesn't really care if his own men get caught in the crossfire. They understand this and don't begrudge him at all. However, much later on suddenly he can't go all out for fear of getting his men hurt. This doesn't appear at all in the light novel, as the first fight has Leon ordering his men to not interfere with his fight and instead assist the allied forces, holding back his full power since he's worried about catching the people he cares about in the destruction, and latter on Leon has no issue fighting alongside his subordinates while still holding back to avoid destroying his own palace and hurting his men.
  • Color-Coded for Your Convenience: In addition to the Primordial Demons themselves, the color of a demonic lineage is commonly used to determine how well things would likely work out when trying to summon one. Red and Yellow demons are Unnegotiable, more likely to trick or kill the summoner. White, Green and Blue demons are Negotiable, the most likely to keep the contract and least likely to screw over their summoner. Black and Purple demons are Whimsical; eccentric, reckless and unpredictable. Sometimes screwing over their summoner, sometimes serving loyally (or fanatically in some cases) and sometimes even giving up the price that they were promised simply because they liked their clients.
  • Complete Immortality: When killed, demons eventually revive in the underworld. Presumably the same for other spirits. However, if their souls are devoured by another demon or someone like Rimuru, they're Deader Than Dead.
  • Covers Always Lie: Some posters show Rimuru, in human form, alongside Shizu. Shizu later dies, and Rimuru doesn't get a human form until he absorbs her following her death.
  • Crime of Self-Defense: The nation that declares war on the city of Tempest? They do so after some of their knights go to investigate a disturbance and see the monsters being struck down by three criminals. Said knights arrogantly announce a one week time frame before launching hostilities... As if Rimuru wasn't already pissed off at that point by seeing a bunch of children among the victims.
  • Crouching Moron, Hidden Badass:
    • Gobta at first glance looks like an idiotic fool who slacks off whenever he can and runs at the first sign of trouble. While he is all that to an extent, he's also the leader of the Goblin Riders of Tempest, an accomplished warrior trained by Hakurou, eventual general in Tempest's military, and capable of performing a Fusion Dance with Ranga to become a True Demon Lord-level fighter who can tear tank armor like tissue paper and shrug off tank rounds powerful enough to kill a dragon like a breeze.
    • Gabiru comes off as a loud-mouth braggart who ends up the butt of jokes due to his own foolishness catching up to him, and while he is he's also the leader of one of Tempest's strongest forces, a master of aerial combat, a brilliant scientific researcher, and becomes a True Demon Lord.
    • Ellen, Cabal, and Gido are a trio of bumbling human adventurers who tend to bite off more than can chew with the only thing really going for them being their luck (and being friends with Rimuru). They become more competent after receiving some nifty gear from Rimuru, but still bumble a bit. In reality, they're all elves disguising themselves as humans from the Sorceror's Dynasty of Sarion, with Ellen/Elyune being the cousin to the "Heavenly Emperor" while Cabal and Gido are actually high-ranking elven warriors assigned as her bodyguards. The reason they appear as "bumbling" is because they seal a good portion of their true strength to hide themselves from possible detection, and they only release it if they're in real danger they can't run or talk their way out of.
    • Bernie and Jiwu are originally introduced as Otherworlders of decent skill that ended up partnering up with Masayuki, hyping the guy up with Hero Worship and coming off as oblivious Yes Men to his discomfort. In reality, they're both Single Digits of the Eastern Empire's Imperial Guard, actually sent to spy on Masayuki and possibly assassinate Rimuru Tempest. Bernie is skilled enough to go toe-to-toe with Benimaru, while Jiwu massacres a whole group of Overcomers (each a Calamity-class monster) and is able to keep pace with Chloe/Chronoa. They also reveal they were playing up the sycophant ways.
  • Cute Monster Girl: Humanoid monster races named by Rimuru tend to become much more human looking, though not always. The small, dopey goblins turn into buff goblin men and cute goblin girls, for the most part, while the ogres shrink in size and become less wild looking. It doesn't always happen, but even several lizardwomen take or can assume a basically human form, depending on whether you're reading the web novel or the light novel/manga.
  • Curb-Stomp Battle: A very common occurance for Rimuru and his citizens. It would be easier to list the fights that don't fall under this trope.
  • Curb Stomp Cushion: The battle in the Labyrinth between Tempest and the Eastern Empire's Armored Remodeled Division of the Armored Corps ends decisively in Tempest's favor, but that's not to say the Empire was completely outmatched. In fact, they managed to defeat 7 of the Ten Labyrinth Lords, with the most impressive feats being how 100 of the division's elites managed to beat Adalman, Albert, the Death Dragon, and their tens of thousands undead soldiers (much of it swelled with fallen Empire soldiers) at the cost of all but the strongest three, and how Major General Minute managed to kill Apito after a hard-fought one-on-one.
  • Dark Is Not Evil:
    • According to Rimuru, demons aren't actually evil even though they're basically darkness spirits. In practice, however, they tend to be sadistic monsters. They are genuinely loyal to summoners that they respect, however.
    • Most of the monster races are shown to not be so different from the other races and can come off as friendly. At one point the idea is floated of reclassifying them as demihumans instead but the idea is dropped. It still implies that (humanoid) monster and demihuman are interchangeable but one is basically just a slur.
  • Defeat Means Friendship: Most of Rimuru's (incidental) way of gaining allies follows the same pattern: Some people pick a fight with Rimuru; Rimuru shows his skill and, if possible, talks to them; Rimuru gains allies. Subverted with the Goblin Tribe because they know fighting is futile, thus surrender as soon as they meet Rimuru and Veldora who can't fight at all but is a very reasonable guy. Utterly averted with the demons he summons, which have all been loyal (if eccentric) Black Demons.
  • Demonic Possession: Demon summoning requires the demon be provided a physical body that requires some form of this, though there are many variants on this. Of course, demons and even spirits in general (though they prefer a more symbiotic relationship over demons) aren't the only race that can pull this off:
    • Have a already-prepared vessel on hand. This can be accomplished with a Golem (as with Berreta) or a homunculus body that has no prior occupant for the demon's soul to settle into and bind to (such as the majority of the Black Numbers).
    • Use a Human Sacrifice. This can involve flat-out providing dead corpses to be sacrificed and broken down into raw material for the demon to construct a body with (as Diablo and his two Greater Demons used the 20,000 or so dead Falmuth soldiers' bodies provided by Rimuru) or a living being choosing to be a Willing Channeler or being Raised as a Host (as was the case with Testarossa before she came under Tempest's employ).
  • Demon Lords and Archdevils
    • Demon lords are individuals from any race that consumed human souls to trigger an evolution into a special almost godlike being. They aren't necessarily demons and, in fact, only one of the ten at the start of the story actually is one.
    • Actual demons are ranked from lesser to greater to arch to peers. Lesser demons are reasonably strong, but both they and greaters are basically fodder. Archdemons are rare, powerful monsters and demon peers are nearly unheard of. The latter are at the same level as demon lords.
  • Disability Immunity: Humans as a race don't usually have access to internal magicule stores like the other races of the world, but this does provide them several advantages that monsters don't. Most significantly, humans are all but immune to the most devastating attacks that directly attack someone's magicule supply (which is partly why Holy Magic, which doesn't rely on magicules but rather faith, has gained its reputation as an "evil-slaying" force), and this allows them to have as many children as they want without fear of losing strength unlike monsters who give up some of their magicules to their children. This also means they can be freely named without consequences compared to how monsters treat getting names as important life-changing events.
  • "Do It Yourself" Theme Tune:
    • The second Ending theme of the first season, "Little Soldier", is performed by Azusa Tadokoro, who is the Japanese voice actress of Chloe Aubert.
    • An odd example in that the first and second Opening themes of the first season ("Nameless story" and "Meguru Mono"), as well as second Ending theme of the second season ("Reincarnate") are performed by Takuma Terashima, who is the Japanese voice of Satoru Mikami, Rimuru's past self long after his speaking role in the series is over.
  • Don't Try This at Home: A disclaimer reading "Never attempt this" pops up as we see Temura dump his computer (plugged in, no less) into the bathtub, as Rimuru told him to do before dying.
  • Early-Bird Cameo: Before Shizue is officially introduced in the episode named after her Shizu, she first appeared during the beginning of the pilot episode, where was sucked into a fire and died... only to be brought into the fantasy world and featured five episodes later.
  • Easily Forgiven:
    • Rimuru has a policy of forgiving people who have disrespected, attacked, or even tried to kill him and putting them to work building up his settlement, though it helps the majority of them (like Vesta and Gabiru) were genuinely regretful for their actions and willing to swallow their pride and degrade themselves to get his forgiveness. Even the orcs, who until their master was defeated by Rimuru were slaughtering and devouring anything in their path to sate their hunger, are shown leniency that surprises everyone, including them. In the case of the orcs, Rimuru even lampshades this before explaining his reasoning; if they continue to fight or take revenge, everyone loses. It's better for the orcs to make up for their actions by deed instead of with their blood.
    • This is subverted, however, against those he deems aren't truly sorry and would simply use his leniency to escape punishment at best or flat-out try and take harmful advantage of him and his people at worst. These ones get a serious beating at bare minimum, followed up by a warning if they're lucky, a quick death if he decides they're too dangerous, or suffer a Fate Worse than Death via assimilation and having their very souls torn apart if he's really mad.
    • He needed the King of Falmuth alive for his future plans but it takes a great deal of escalating restraint on his part when the King starts off simultaneously begging for mercy and rebuking Rimuru for talking down to him, then proceeds to ceaselessly spitout a nonstop diatrab of obvious lies, blame-shifting and ridiculous nonsensical excuses after Rimuru unleashes a deadly energy aura in response. When the king starts trying to negotiate for post-war reparations of lost troups after being assured he wont be killed, Rimuru finally loses his patience and blows off his arm to get him to finally shut the hell up.
  • Egopolis: Defied by Rimuru, who objects to the capital city of the Jura Forest Alliance being called 'Rimuru', but played straight when everyone calls it that anyway.
  • Ethnicity Monarch:
    • Benimaru and his sister Shuna are the prince and princess of the oni (later Kijin) race.
    • Gabiru and his family are the rulers of the lizardfolk (later Dragonnewt) race.
    • Geld is the name held by two different leaders of the Orc (later High Orc) race.
  • Even Evil Has Loved Ones: Light novel volume seven opens with Clayman's friends and allies mourning his death. Their grief is deep and genuine, exacerbated by the fact that they cannot prosecute vengeance on his killer due to a lack of manpower and resources.
  • Evil-Detecting Dog: Played for tragedy in Shizu's backstory. Her friend adopted a stray animal and tried to keep it as a familiar but it started growling at Leon so Ifrit burned it and Shizu's friend to ashes.
  • Evolutionary Levels: Every species has higher forms they can evolve into. Mostly the change is linear but there can be variants sometimes.
    • Goblins evolve into Hobgoblins (for the males) and Goblinas (for the females).
    • Humans after overcoming several odds can evolve into Sages, who in turn evolve into Saints.
    • Rimuru himself evolves after some time into a Demon Slime when awakening into a True Demon Lord and later he becomes an Ultimate Slime, reaching the pinnacle of his species.
    • Ogres can evolve into Oni if they attain enough power and can further evolve into Fair Onis or Evil Onis.
  • Evolution Power-Up: All lifeforms in the world are able to do this, acquiring more power the more they evolve.
  • Exact Words:
    • Gelmud tells Geld to evolve into a Demon Lord already. Geld fulfills his request by killing and eating him, prompting his evolution.
    • When the elf does her fortune telling for Rimuru, she shows him Shizue as "the one destined to be with you". She literally gets eaten by Rimuru, offering him his humanoid form.
    • Hinata was told that Rimuru was the one responsible for Shizue's death and thus goes after him in order to avenge this crime. Rimuru admits that it's technically true since he both removed the spirit Ifrit which was keeping her alive and devoured her body per her dying wishes, but is not given time to explain or elaborate before Hinata attacks. Even when he tells her there were extenuating circumstances, she retorts that she doesn't care and that only the end result matters.
  • Explain, Explain... Oh, Crap!:
    • When Gabiru arrives in the village, he tries to convince Rimuru that the goblin village should become his subordinates because they are so weak. However as he is explaining this he starts to notice that his audience is a hobgoblin, a slime and a group of evolved ogres, and not a weakling goblin in sight.
    • When going over the information about the Orc Army, they start to wonder how an army of thousands of Orcs are able to stay supplied. They then realize that every area they go through there isn't a single body found be it Orc or other monster. It is then they realize that the Orc army is eating the bodies of anyone slain in battle.
    • If anyone who has some knowledge about demons end up fighting Diablo, you can expect their Inner Monologue to end up like this. It really doesn't help that Diablo likes toying with his enemies as they go through a slow realization.
  • Extremely Short Timespan: While most of the story arcs take place over a few days, weeks, or even months, the arc where Rimuru and co. finish things up with Clayman, including the decimation of his army, conquering of his castle, and face-off between Rimuru and Clayman, all happen over the course of a very eventful but relatively small number of hours.
  • The Federation: Rimuru was initially the central figurehead of The Alliance between the various monster races of the Jura Forest, but after the defeat of the orcs, the proper foundation of Tempest, and his True Demon Lord ascension/recognition, the nation eventually turned into this as his rule was solidified over the forest and the races pledged their loyalty to him.
  • Fictional United Nations: The Council of the West is basically a medieval version of the UN, albeit with more actual authority and power. It's made up of many western human nations that originally banded together as a cooperative force against monsters, but eventually grew into a political force meant to counter the growing power of the Eastern Empire and provide the western nations a bulwark against the Demon Lords while having power over its members' international affairs and meditating over internal conflicts. It doesn't technically have a standing army of its own (though it can call upon the militaries of its member nations in times of crisis), but rather relies on the mutual cooperation of the Adventure Guild, which they are the main funder of in exchange for being able to call upon its members as a police force (in fact, both the Council's and the Free Guild's headquarters are located in Ingracia just to drive this home). This funding in turn comes from the contributions provided by the member nations, which varies depending on how many councilors said nation provides to represent their interests (in other words, the more you're willing to pay, the greater your voice in international matters). This bloc does not include Dwargon, Sarion, or Ruberios, as all have sufficient military and economic strength to act independently of the Council, but they maintain cordial relations if nothing else. Joining the Council is a marked interest of Rimuru, as doing so would open plenty of doors to the international trade with humans he craves and thus it's a major goal of the Rosso family to prevent him from doing so (or at least, only on their terms), as they recognize that Tempest's prosperity would easily lead to it gaining disproportionate power on the human nations that would threaten their own power.
  • Formula with a Twist: It's Exactly What It Says on the Tin: the protagonist is reincarnated as a small slime—albeit with a very powerful ability to copy the powers and properties of any person or thing it devours (as well as an unseen "Sage" that provides other useful powers and information).
  • A Form You Are Comfortable With: Rimuru often takes human form when talking with humanoids so that they can more easily conduct conversation. In some cases this backfires, with visitors seeing him as a mere slime trying to imitate a person.
  • From Nobody to Nightmare: Two nations on a geopolitical stage.
  • Generic Doomsday Villain: Kagurazaka Yuuki in the web novel doesn't really have any kind of decent motivation. He just wants to destroy the world because he wants to destroy the world. There's a vague acknowledgement that he maybe had a tough childhood or something but even the characters don't believe that this makes any kind of real sense. There's actually some setup for him being more than this during the middle part of the story, but in the end it's all scrapped and he's just all "MWUAHAHA I will burn everything!" In later adaptations he settles for the more mundane Take Over the World with a side of Well-Intentioned Extremist.
  • God-Eating: Rimuru practically starts out doing this by absorbing the sealed Veldora Tempest via [Predator], though this was a willing act on both parties' ends as doing so would allow him and Veldora to analyze the Unlimited Imprisonment at their leisure and eventually free Veldora. In a much more serious manner, Rimuru ends up having to do this again on a Brainwashed and Crazy Veldora during the war with the Eastern Empire to put him in a position to free him from the brainwashing. This time, the act of breaking down Veldora's potent magicules directly actually causes Rimuru (who has grown much stronger since then) physical and spiritual pain, but this also ends up in Rimuru properly assimilating Veldora's magicules and becoming a True Dragon/Ultimate Slime himself. And then for good measure, Rimuru does the same thing to Veldora's brainwashed and pissed-off sister Velgrynd to free her of the former and calm her down by showing her brother's okay.
  • Harem Genre: Hilariously subverted, as while Rimuru identifies as male, admits that he would want to finally give up his "virgin" status, is very much an admirer of the womanly form, and there's no shortage of interested females, his "little brother" no longer exists. Though he does admit even that with his shape changing ability, that is entirely by choice.
  • Holy Burns Evil: Played with by Holy Magic, which at first glance fits this trope due to being far more effective on monsters than it is on humans and thus gains the reputation as a "purifying" force that destroys "evil" monsters. In reality, Holy Magic works by using "faith" to power magic that manipulates holy energy, purifies magicules, and at high levels manipulates "spiritrons", the very building blocks of magical energy. As most humans have little to no magicules at all while often times most monsters don't just rely on magicules to survive but they're partially made from them, this makes all but the most powerful Holy Magic spells devastating to monsters while mostly harmless to humans. This is why many beings tend to react in shock if they see a monster casting Holy Magic, as even if they know it's technically possible, without fine-tune control and/or a Skill that provides resistance against Holy Magic's effects it's basically the equivalent of throwing around radioactive material and praying they don't kill themselves in the process.
  • Holy Hand Grenade: Holy magic in this story follows a similar path of Religion Is Magic, where fervous belief in a higher power allows one to cast powerful attacks that bypass Anti-Magic and are capable of even killing the soul, though in this case it's closer to Clap Your Hands If You Believe in execution, as the idol of worship does not need to be divine themselves, the caster simply needs to have absolute faith in the chosen person in order to power their holy abilities.
  • Honour Before Reason: Benimaru in his first appearance where he fights against Rimuru even after he realizes the gap between their respective abilities. At this point, he's one of six ogres still alive after the orcs slaughtered his village as well as their acting leader and should be prioritizing the safety of his followers over recklessly endangering them fighting a foe he assumes is responsible for leading the orcs, especially after said foe incapacitated three of them without using anywhere near his full strength. Luckily, Rimuru's an understanding chap.
  • Humans Advance Swiftly: Most monsters have telepathy, so they don't use maps or writing, resulting in them not being able to pass much knowledge onto their children if they don't have time. Humans also understand their physical and magical weaknesses compared to monsters and thus are firm believers of unity to stand against them, resulting in humans being far more likely to forge alliances with each other or even neutral monster nations than their monster counterparts.
  • Humans Are Average: Most humans appear to be "normal" humans, without natural access to magic or even natural internal magicule supplies, though it's possible to develop such aptitude. On the whole, humans are physically and magically weaker than monsters, but they have the potential to far outnumber them and they've leveraged their technology and knowledge to develop countermeasures.
  • Human Jungle Gym: The spin-off work The Slime Diaries has Rimuru visiting Geld II, the orc in charge of Tempest's construction efforts, and finding at least seven tiny goblin children climbing all over him, since they like to play with him when he takes breaks from his work. It is ridiculously adorable.
  • Human Resources: The Summons, who are yanked from other worlds by many nations and powers of this world more-or-less on an industrial basis for the slim chance of producing a Hero-level warrior that might be used against monsters or rival powers. Note that the Summons who fail to develop into heroes usually die within several years as their bodies cannot stand the enormous level of mana acquired in the process.
  • Human Sacrifice: Rimuru needed to kill more 10,000 and devour their souls to evolve into a True Demon Lord. He did this by killing the invading army of Falmuth that numbered 20,000.
  • Humble Hero: Rimuru wisely presents a humble front to everyone he meets, although he makes sure people understand he is a ruler of monsters. This gets him criticized by the Dwarven King, who warns him of the consequences of making himself too humble as king of a nation.
  • I Did What I Had to Do:
    • The Orc Lord admits he was aware that Gelmud was using him in an Evil Plan, but tells Rimuru he didn't have a choice. His people were dying from starvation, and he couldn't save them any other way.
    • Rimuru himself undergoes this when he slaughters the invading Falmuth army, despite knowing some of them were simply Just Following Orders and My Country, Right or Wrong. He doesn't take pleasure out of any of the killing, but it's the only way he'll gain the power necessary to evolve into a True Demon Lord and revive his fallen people (including Shion).
  • Infinity +1 Sword: The aptly named Legend and Mythical/God-grade weaponry and armor are this, and fittingly are wielded by the strongest beings on the planet. The former is described as so overpowered that "owning one is akin to bringing a machinegun into swordfights", while the latter is equipment that only Physical Gods could use to their full potential.
  • Immortal Procreation Clause: Monsters and humans that live longer than humans tend to have significantly lower fertility. Demon lords in particular turn out to be sterile. Several races like elves and oni reproduce very slowly not just because of biological limitations but also social ones, which keeps their populations barely at the level of sustainability. Benimaru has to delay his evolution as it would have him reach the pinnacle of evolution possible for him, thus ‘ridding him of the need for procreation’, and as one of the last of the ogres he needs to have children. He only evolves after producing heirs with Momiji and Albis.
  • Insistent Terminology: Rimuru repeatedly states that his escapades with Milim, Veldora, and Ramiris into The Labyrinth and griefing parties with their monster forms are "research", not "games", and that there's plenty of importatnt things they're obtaining from this like fine-tuning the Labyrinth's difficulty through first-hand experience and training themselves with limited skillsets. He gives up when even Raphael calls them "games" to his mental face.
  • Interspecies Romance: Several humanoids develop crushes on other races, such as Soka having a thing for Souei or Garm being interested in Shuna and getting very confused around Rimuru.
  • Kangaroo Court: Trials in the Armed Kingdom of Dwargon are essentially this, as the defendants are not allowed to speak in their own defense and must rely on a proxy to speak for them, which of course leaves the proxy open to being bought, as we see with the trial of Kaijin, Rimuru, and Kaijin's brothers. The irony being the king knew this was a sham trial and used it to allow the defendants to leave the city without issue, while also lambasting Vesta for not manning up and admitting his own fault in private that leaves him thoroughly ashamed of himself.
  • The Legions of Hell: There are two noticeable examples. The first are the demon legions under Guy Crimson who are ostensibly one of the biggest threats to human civilization, but Guy isn't interested in outright eradication and instead uses them for "raids" to keep humans on their toes. The second are the Black Numbers who make up some of the strongest demons on the planet directly under Rimuru, which technically makes them the good (or at least neutral) guys.
  • Let's You and Him Fight: Both fights between Hinata and Rimuru come down to this in the end. In the first one, the ones behind it were hoping Hinata would kill Rimuru by feeding her Metaphorically True information that painted Rimuru in the worst possible light. In the second one, they were hoping Rimuru would kill Hinata by forcing a situation where they would both believe the other side had come to do battle again rather than peace talks like they both really wanted, manipulating available information and making both sides assume the worse of each other.
  • Loads and Loads of Races: More or less standard Medieval European Fantasy set with some additions, which seems to be inspired by the Monster Quest.
  • Loophole Abuse: The Resurrection Bracelets are explicitly designed so that they only work while inside Ramiris' Dungeon, so taking them outside would be useless as they wouldn't grant resurrection (as Rimuru and staff warn adventurers who are challenging the Dungeon). However, there's nothing saying that you can't teleport to the Dungeon while wearing the bracelet to escape a fatal wound via the Dungeon's resurrection system, as Gadra successfully finds out.
  • Meaningful Rename: If a demon/monster is named by a strong individual, he/she gains some power from the name but it also means the giver has to give up part of their magical power (though luckily, magical power can regenerate with time). That's why monster parents don't name their kids.
  • Medieval Stasis: Enforced by angels who descend every 500 years in massive armies that destroy any civilization that exceeds a certain level of development. Dwargo used to be the only survivor of such an assault before Tempest came along. As a result, technological progress usually has to be done in secret and selfishly hoarded by most nations researching it. Otherworlders that aren't being summoned as weapons of warfare have actually found use providing what technological knowledge they possess to their new nations. The Eastern Empire, for example, has been using their Otherworlders' knowledge to produce working modern-day guns to better build up and supplement their military might in preparation for a war with the West.
  • Medium Blending: Rimuru's interface with the Great Sage is made up of CGI and live film of water and various objects.
  • Monster Town: The Goblin Village. Under Rimuru's leadership and the help of a growing number of advisors, more and more races join the expanding village until it becomes an outright Monster Nation known as Tempest.
  • Muscles Are Meaningless: A monster's power is tied to their magicules, not their physical bodies. For example, Benimaru got a huge power jump by evolving from an ogre to a kijin even though he got physically smaller. And then you have the likes of Milim, whose physical strength lets her send people and things flying with ease despite having a build of a petite female teen at best.
  • No Biological Sex:
    • Demons don't appear to actually have fixed genders. Guy can switch between a male and a female form as he pleases, though he defaults to male. Diablo seems to have no sex at all, though 'he' is beautiful either way and presents as male. Carrera, Testarossa, and Ultima are either all-female or simply choose to look that way.
    • Slimes by default don't have any fixed genders or sexes from both not needing sexual reproduction and as a rule just plain not sentient enough to acknowledge such things.
  • New Life in Another World Bonus: Beyond just Rimuru, people from Japan getting transported to the other world is actually a common occurrence, though Rimuru's method of getting there by dying and coming back as a different species is an unusual case. People from our world get a huge magical power boost whether they ended up there by chance or by being summoned, though those who were summoned are not as powerful as the former, and those who were summoned as children are unable to properly use their powers and die unless they bond with a strong spirit to help them control their powers.
  • Odd Friendship: A slime and a dragon? Who would have thought it?
  • Older Than They Look: Most Demon Lords look like they're in their 20s-early 30s but have lived over a hundred years at least. Milim is an excellent example as she looks and acts like she's in her early teens but is stated to be the strongest and oldest of the Demon Lords.
  • Our Cryptids Are More Mysterious: Introduced very late in the light novels, the Cryptids are an ancient race of monsters born from the magicules of World Destroying Dragon Ivarage and are native to the Otherworld he's been sealed in by Veldanava and watched over by the angels. They come in two types: Insect and Beast, and as a rule they are extremely powerful yet thoughtless monsters who live to fight and dislike working together. The Insect types would break off and become the Insectar race (the same race Razul, Apito, and Zegion belong to) after the birth of the sapient Insect Lord Zelanus. Dino implies that Kumara and by extension her mother are also sapient Cryptids.
  • Our Demons Are Different: They were originally called Dark element spirits and are spiritual lifeforms that dwell in the underworld. They only appear in the material world if summoned and quickly disappear if not given a suitable physical vessel as it takes a lot of energy to maintain themselves in the material world, though as a trade-off while they're still solely spiritual beings they're immune to physical attacks and can only be harmed by magic and Skills.
  • Our Dragons Are Different:
    • They are among the most powerful races in the whole setting, "descended" from the True Dragon Stellar King Veldanava. They can take various forms, but they mostly resemble Western Dragons physically and start off as rather dumb beasts, but grow stronger and smarter as they get older. The final evolution of the line are Dragon Kings/Lords, who have the ability to take a humanoid form. There are four 'types': fire, ice, wind, and earth, though some can obtain special evolutions through various circumstances. The Sky Dragon Rimuru fought was an aberration of the wind type, while the Death Dragon who works with Adalman is a dragon that lost its original typing when it became an undead.
    • The True Dragons, however, are another beast entirely. Whereas normal dragons are still flesh-and-blood beings to an extent, the True Dragons are spiritual beings who are more akin to sentient forces of nature and gods, and there can only be one specific type of True Dragon at a time as designated by The World. If one dies, it will eventually resurrect (albeit with some memory loss) save in very specific circumstances.
  • Our Dwarves Are Different: Dwarves in this setting are basically humans with beards, who have a cultural fondness for mining and crafting. Their kingdom is 10,000 years old, and fairly cosmopolitan, allowing fair treatment of any being who can get in the gates. Also, while they are usually short and wide, there are several such as Vesta and Gazel who look like they could pass as humans such is their height and generally slimmer forms. They're technically descended of fairies who were incarnated into the physical world and were aligned with the Earth element.
  • Our Elves Are Different: Elves are a Long-Lived race that, depending on how pure ones' blood is, allows them live for centuries or even thousands of years in their physical prime of the 20s before old age rapidly catches up to them in their dying years. This is due to them being strongly associated with the divine powers of their fairy ancestors that incarnated and were aligned to the Wind element. Once in the distant past, the elves were magically and technologically one of the most powerful races in the world with one of the most powerful kingdoms. Then they made the mistake of trying to control the Dragon Princess Milim Nava and murdered her pet dragon in the process. Milim destroyed their nation in a rage while ascending to True Demon Lord status and the freak revival of her pet as the Chaos Dragon put an end to any hope of the elves reuniting and scattered the survivors to the winds. Some settled in the Forest of Jura and became the equilvalent of Wood Elves, the most successful faction created the Sorceror Dynasty of Sarion as the High Elves, and one of the surviving elven nobility known as Kazaream established the Puppet Nation Jistav for those that would become the Dark Elves.
  • Our Goblins Are Different: The goblin tribe Rimuru originally meets are short and weak physically like children, though they are clever and skilled enough to quickly erect fortifications as well as use basic weapons like spears or bows. After he names them, they transform into Hobgoblins and Goblinas for male and female respectively, who essentially resemble green-skinned adult humans with developed canines and pointy ears save for the actual children. Except for Gobta, who still appears the same ("My growth was more of a spiritual type!). Personality-wise, however, they're practically no different from tribal humans who have no issues with coexisting with former enemies in peace. They're also descended from fairies that incarnated into the physical world and were aligned with the Fire element, but unlike elves or dwarves they're retained very little of the divine power of their ancestors and hence their comparatively far-shorter lifespans.
  • Our Ogres Are Different: They're multicolored horned humanoids, whose weapons, armor and architecture are distinctly Japanese in style. Rimuru notes with surprise on first meeting them that they're not the brutes he'd expect based on other media. Also, they're actually considered evolutionary a step-up from goblins, and can evolve themselves into Oni.
  • Our Orcs Are Different: At first, not much different, as they are Always Chaotic Evil in their first appearance and are a huge source of trouble for the main characters. It is revealed they are under the influence of "Starved", a special skill which fills them with an overwhelming hunger. Once the Orc Lord is defeated, they lose these traits and just become a race of The Big Guy. Their appearance is that of the Pig Man.
  • Our Souls Are Different: The "soul" is the name given to the spiritual being of humans and monsters, the very core of a person through which there is no deeper "being". It consists of three parts: The Nucleic Heart (the core of the soul where Skills are engraved), the Ego (which is where the memories and sense of self are stored), and the Astral Body (the container for the soul and the form of a being), the last of which requires the actual "body" (be it spiritual and/or physical) to hold everything together and be called "life". The soul is what undergoes the process of Reincarnation and usually begins to degrade as soon as the body dies, but certain beings have the innate abilities necessary to endure and survive on as spiritual beings without their flesh, at least for a time.
  • Our Vampires Are Different: They physically resemble humans who need to drink blood to survive, although this ceases to be a necessity once they reach a sufficient age and power level, and they don't even need to fully drain a person to support themselves. They follow an aristocracy. They also have their powers weaken during a new moon. They possess various classic powers such as Super Strength, transformation, regeneration, and hypnotism. Notably, they were technically a Dying Race at one point since their population relies on the well-being of humans, which ended up devastated by massive wars and Veldora's indiscriminate rampages, to the point that their Vampire Monarch founded and set herself up as the shadow ruler of the human-centric Holy Empire and god figure of the Western Saints Church while also creating an underground kingdom for her people so they could coexist peacefully and in secret.
  • Perfectly Cromulent Word: The "Beastketeers" of Yuurazania, a combination of the words "Beastmen" and "Musketeers". They act as a kind of Praetorian Guard for their liege, the Demon Lord Carrion.
  • Personality Powers: Unique and Ultimate Skills are effectively this crossed with Soul Power, as unlike the lower tiers of Skills (which can be obtained between beings of the same race or may be held by otherwise different beings) their effects are effectively reflections of the personality and soul of their holders. For this reason, there can't be two holders of the same Ultimate Skill living at the same time, and while it might be possible (though unlikely) for more than one person to possess the same Unique Skill in name, the specific effects of it will likely be different between users. The only exception would be possessing the ability to somehow copy said Skills, and only Guy Crimson, Rimuru, and Yuuki have the Skills or abilities to do that.
  • Plant Person: Dryads are very rare and the 'C.E.O' of the Great Forest. Treants are also mentioned.
  • Power Equals Rarity: As a world building trope in the setting. Regardless of what it is, generally the rarer something is the more powerful it tends to be. Whether it refers to powerful species like Ogres and Tengu who are dwarfed in population numbers by much weaker species like goblins or items that increase in power based on who rare they are such as potions and weapons, it hold true. The most egregious application is seen in skills. Rare Skills are stronger than more common ones. Unique Skills host a plethora of lesser Skills within them and cannot be blocked by any skill that is not itself a Unique or Ultimate Skill. Speaking of which Ultimate Skills are even rarer still and grant Reality Warper powers to whoever has one, making them immune to basically anything that is not itself an Ultimate Skill.
    • The power of Ultimate Skills far and away dwarfs unique skills, not just in terms of effect, but also intensity. [Unlimited Imprisonment] would have taken a century to be undone by Rimuru's [Great Sage] and Veldora's [Investigator], but once they became the Ultimate Skills [Raphiel] and [Faust] it was undone in less than a day.
  • Power Levels: They exist and are used to mainly classify monsters to give a rough estimation of their strength. However, Slime pokes fun at the concept because these values and the rankings therein only take into account a being's physical ability, their mana/magicules, and the power of their equipment, not anything that's related to actual combat ability (combat experience, training, magical knowledge, willpower, and Skills). Hakurou even after his evolutions would only be about mid-tier in terms of power, yet it's his experience and skill that lets him reliably beat those with three times his level. The system itself was also technically created by humans, but they woefully underestimated just how strong some monsters can become due to how few humans can even force a Demon Lord to get serious, let along go all-out (for reference, the minimum requirement to become a Demon Lord would be to have an EP of 200,000. Clayman, one of the weakest Demon Lords active, has an EP of around 400,000 even before his last-ditch True Demon Lord awakening, and most of the True Demon Lords are at least over a million).
  • Powered by a Forsaken Child: The only reason Rimuru was able to get away with his crazy naming sprees was because he was unknowingly draining magicules from Veldora imprisoned inside him.
  • Prophecy Twist: Rimuru has his fortune of a woman he is destined to be with. He assumes that this means lovers. Said woman actually dies shortly after he meets her, but her dying wish is that he assimilate her.
  • Quality over Quantity: Tempest vs almost anything else. Examples are aplenty:
    • Falmuth came at them with over 20,000 troops plus an assortment of Temple Knights from the Church, but 113 named monsters (Rimuru, Benimaru, Souei, Souka, Touka, Saika, Nansou, Hokusou, Gobta, Rigur, Geld, Hakurou, Gabiru and Gabiru's 100 followers) proceeded to utterly destroy their forces. Heck, Rimuru wiped out the 20,000 Falmuth forces on his own.
    • The quality of Tempest equipment is unmatched in the world, with two of the greatest blacksmiths on the planet working with pride, as well as a few dozen proteges training under them. Compared to other nations who had dozens on hand, but cannot hope to match the quality of the best Tempest goods.
    • The full potions and high potions play on this, while high potions are mass-produced, they are done so with the far harder-to-produce full potion being diluted in magicule-rich water to produce 40 of them. This process is the most resource-efficient, but also the most difficult to achieve. Full potions are not widely available for sale due to their insane cost of 5 gold coins, over 14 times the cost of a high potions 35 silver, and 125 times the cost of a low potions 4 silver.
    • Invoked on a mass scale by the Eastern Empire, to the point it disturbs Rimuru after the fact despite understanding the logic behind it. Emperor Rudra, Velgrynd, and Tatsuya Kondo have no issue with nearly a million soldiers of the Armored Division being wiped out to a man if the resulting slaughter would invoke a Traumatic Superpower Awakening in even just about a half-a-dozen specific individuals to the level of Demon Lords, considering that a net positive. In fact, they have a precedent for it with the first failed offensive against Veldora in the distant past. The only thing they didn't anticipate was Tempest managing to be completely thorough and Kill 'Em All.
  • Quirky Miniboss Squad: Various Demon Lords have some variant of this, often well characterized and given screen or page time to develop their personalities.
    • The Beastketeers under Demon Lord Carrion.
    • The Five Fingers under Demon Lord Clayman.
    • The Moderate Jester Troupe under Demon Lord Kazaream
    • Rimuru originally, ostensibly, had the Big Four. Later he formed the Twelve Guardian Lords.
  • Reality Warper: Technically, anyone who possesses an Ultimate Skill is automatically one. According to Guy Crimson, all the natural laws that rule the world are "nothing more than unique cases to them", as Ultimate Skills give the wielders fittingly ultimate power to control the very laws of nature and can only be countered by another Ultimate Skill.
  • Recap Episode: Episode 24.5: "Tales: Valdora's Journal" takes place right after Rimuru absorbs Ifrit. Valdora is quite pleased to see a formidable opponent to join him, and immediately teaches him how to play Shogi. The episode takes place over the two years that have passed in the first season. While clips of the entire first season up to that point play out, the two engage in banal conversation that has almost nothing to do with Rimuru's progress, though they do give a general recap of the major story arcs. They're just enjoying each other's company while playing Shogi.
  • Reincarnation: They're rare but have enough presence that people know what the deal is with them (i.e. they have power, be it skills or resistances, based on the conditions they died in and their choices). Rimuru and Shizue are known examples. People who are reincarnated are given a choice of what kind of power is blessed to them by the "Voice of The World" in addition to a blessing of power based on the conditions they died in. Most of them tend to retain their original form, however, which is why Rimuru's accidental rebirth as a slime is noted to be rather odd.
  • Reincarnate in Another World: It's right there in the name, and these specific type of Otherworlders are explicitly called "Reincarnators".
  • Rite-of-Passage Name Change: Monsters typically don't have individual names, the only exceptions being leaders and the direct subordinates of leaders. This is because named monsters receive a massive boost in their Power Levels, their boost proportionate to the ones who named them. When Rimiru named all the goblins and direwolves in the village, they all evolve into Hobgoblins and Tempest Wolves.
  • Running Gag:
    • In The Slime Diaries, after Gobta remarks how delicious slimes are, with Shuna and several other characters agreeing, Rimuru — who sees them surround by an aura of killing intent — jumps to the conclusion that they're plotting to eat him and runs away as fast as he can. This is referenced a few times, with Rimuru low-key panicking whenever characters comment how delicious food shaped like him is in a way that sounds like they're talking about him.
    • In The Slime Diaries, whenever a scene starts between Milim and Shion, Milim always refers to Shion as "one-horn lady", which acts as a sorta Phrase Catcher for Shion to say "it's Shion", followed by Milim saying "yeah, that!" This humorous example of Milim's Accidental Misnaming habit happens every time the two have a conversation.
  • Sealed Evil in a Can:
    • Veldora might not be "evil" in the moral sense, but his indiscriminate destructive rampages were so dangerous for the world that few people had issues when the True Hero used her Unique Skill Unlimited Imprisonment to seal him away.
    • The Holy Ark that is the most secret and prized treasure of the Holy Empire of Ruberios is actually the sealed body of said Hero, Chloe/Chronoa, partially to prevent the Chronoa personality from taking over without resistance while Chloe and Hinata's time-displaced souls are indisposed due to their current selves still being in the present timeline.
  • Seven Heavenly Virtues: Represented by the virtue series of ultimate skills. Each of them is named together with an archangel. Collecting all skills of this series would allow its user to unseal the Mind of the Angels. There is also a secondary effect of the virtue series skills, namely that anyone who has one is vulnerable to being put under Mind Control via Justice King Michael.
    • Justice King Michael wielded by Emperor Rudra, later claimed by Velda
    • Wisdom King Raphael wielded by Rimuru
    • Covenant (Faith) King Uriel wielded by Rimuru
    • Purity King Metatron wielded by Leon Cromwell
    • Patience King Gabriel wielded by Velzard
    • Hope King Sariel wielded by Chloe O'Bell
    • Charity King Raguel wielded by Velgrynd
  • Seven Deadly Sins: Represented by the Sin Series of the ultimate skills. Each of them is named together with an Archdemon. Collecting all skills of this series would allow its user to unseal the evolution tree of the Demons
    • Lustful King Asmodeus used by Ruminas Valentine
    • Gluttonous King Beelzebub used by Rimuru Tempest
    • Greedy King Mammon used by Kagurazaka Yuuki
    • Slothful King Belphegor used by Dino
    • Wrathful King Satan used by Milim Nava
    • Envious King Leviathan used by Ice Dragon Velzard
    • Prideful King Lucifer used by Guy Crimson
  • Serious Business:
    • Offering to name someone is this from a monster's perspective. Naming a monster involves imparting one's magicules to the recipient, which has the risk of weakening (or even killing) the namer through magicule drain if they name too many at once or name someone too strong.
    • Declaring yourself a Demon Lord or a Hero is this for monsters as well. To call yourself the former is to stake your claim that you deserve a seat at the Demon Lord Council, and if no existing members are willing to vouch for you, you can expect an actual Demon Lord to show up at your doorstep to test you personally. Proclaiming yourself the latter is implying that you are the destined rival of the Demon Lords who will stand up to them if they get out of hand, and will get much the same reaction. That's why most humans use the term "Champion" instead.
  • Shout-Out:
    • When testing out his newly-acquired Steel Thread ability in the anime, Rimuru lets out a Tarzan yell.
    • The design and animation of Ranga's father brings Kiba to mind.
    • In Episode 6, Rimuru tries to break the ice with the adventurers by saying "I'm not a bad slime!", which is a line friendly slimes in Dragon Quest tend to say as a greeting. Shizue cough-laughs, and later reveals she knows the line is from a video game thanks to another reincarnated person she knows.
    • In Episode 20, Haruna and the main Goblin Cook sprinkle salt onto a sliced up Megalodon while striking the same pose as the "Salty Bae" meme.
      • Also in episode 20, Rimuru and Yuuki discuss among other things Ah! My Goddess's anime, what number "FF" is up to, and the fact that Glass Mask is still going.
    • In the Christmas episode of The Slime Diaries, Milim uses a Thunder Cross on Rimuru after mistaking him for Santa Claus.
    • In Episode 47, Rimuru orders Veldora to keep Milim at bay during their fight against Clayman. When he gets enough of a breather to check up on Veldora, he's seen spamming Hadoukens at Milim, then pursuing her in the air with a Shoryuken, Tatsumaki Senpukyaku, and a Tetsuzanko, finally ending his "combo" with a Kamehameha. Rimuru can only watch in exasperation, wondering out loud where he larned all those special moves.
    • The God Series of Ultimate Skills are named after the Great Old Ones and Outer Gods of the Cthulhu Mythos.
  • Showy Invincible Hero: Tempest rarely struggles and essentially never loses. Rimuru himself has only lost a single legitimate fight, with all others being victories or he was smart/clever enough to make his opposition give up non-violently despite their possible advantage.
  • Sitcom Arch-Nemesis: Between Shion and Diablo. Mainly because they are both Rimuru's secretaries. Despite the demon's greater intellect, experience and power, he shares the same mindset as Shion (ie Leave No Survivors as the first option) so both tend to offer the same sort of solutions. They both needle each other as Diablo is far more useful in various tasks but Shion is much closer to Rimuru.
  • Sneeze Cut: In Chapter 89 of the manga, when Rimuru notes to Gabiru how he's going to be joined by the skeletal Adalman in Veldora's cave, to which Gabiru responds with a shocked shout, the following panel has Adalman coughing in a sneeze-like way despite lacking sinuses.
  • So Last Season: The story can go through this quickly as a result of Rimuru and his followers gaining more strength from foes either joining their cause or being absorbed to add their power to Rimuru's. As an example, a lesser demon puts up an okay fight against Rimuru, then he summons a greater demon to inhabit a golem. Next is an archdemon, at which point greater demons are total loser small fries. Then archdemons become fodder to hype up Demon Peers, who break this trope without even trying. Guy Crimson falls into the 'Demon Peer' catagory, and everyone is cautious of him.
  • Spell Blade: There are several variations of this.
    • The first is to channel and wrap your own magical energy around your weapon like a "sheathe". Rimuru technically first did this when Great Sage coated his katana in Black Flame during the fight with the Orc Disaster, and he later did this himself when he shrouded his sword in magical energy to defeat a summoned demon during his Adventurer Ranking test (as the demon was otherwise immune to physical attacks and he didn't want to launch a massive magical attack or use Gluttony in full view of a bunch of strangers). This method can be taxing for the average person to use for very long, however, and is usually only really practical with magisteel or similar weapons.
    • The second is to carve magic runes into the weapon during or after its creation. By activating the runes, you can then use the elements in question. While less magical taxing and in theory anyone could use such a weapon, however, the problem is that a weapon can only take at most two different runes before being ruined, and it's impossible to remove the runes once they're carved in. Rimuru can do a variant of this by using the Unique Skill [Degenerate] to merge the magic of choice directly into said weapon and switch it out at will, but obviously this is something only someone with a similar Skill could reliably do.
    • The third is to simply let your weapon evolve with you. This however takes lots of time, can only be done with a high-quality magisteel weapon, and there's no guarantee that you'll get the exact traits you want when it starts evolving.
    • The fourth is one of Tempest's creation, involving creating weapons with sockets in them (a maximum of three) that one can insert Power Crystals containing various magics at will. By mixing-and-matching magic cores, you can strengthen or create various combinations of elements. The only cost is that this is a hard weapon to craft; only Kurobee can reliably make the three-slot weapons (and even then that's one in a few hundred attempts), Kajin can only get up to the two-slots, and even the very best apprentices are lucky to successfully make one-slot weapons.
  • Spoiler Opening:
    • The first anime season's first OP has a number of minor spoilers here and there with the most notable one being that Rimuru will gain the ability to shift in and out of a human form.
    • The second anime season's first OP continues this, such as showing a glimpse of Veldora's human form, Milim's Battle Mode, and Wisdom King Raphael, all of which only first appear in the last two episodes of the first half of the season.
    • The second opening of same season also showing the remains Great Demon Lords like Dagruel, Dino and Luminous Valentine
  • Standard Japanese Fantasy Setting: Set in an RPG Mechanics 'Verse that mainly draws from medieval Europe but has a cabal of demon-lords and heroes who are often summoned or reincarnated from other universes. The main character, Satoru Mikami, is reincarnated as a slime dubbed Rimuru Tempest. He becomes the leader of a village of goblins (which evolve into hobgoblins), gradually accruing more followers of different monster species — including ogres (which evolve into oni), pig-man orcs, and lizardmen (which evolve into dragonewts). He also forges dipilomatic relations with some of the neighboring human and dwarven kingdoms; befriends dragon-gods, heroes, and demon lords; and wages war against a corrupt church and the kingdoms under its sway.
  • Stronger with Age: A general rule of reality in this work. The older something is, the more powerful it is. Even true of ostensibly mortal races like humans; once they reach a certain level of power, they evolve into stronger forms with longer lifespans. Any human say, 300 years old, is much more powerful than an average joe. A sufficiently aged unnamed monster can defeat a younger, similarly ranked one that even has the extra advantage of a name for a power boost, as proven when Diablo when he was still unnamed as Noir defeated Orthos despite both of them being the same rank at the time with the latter being named.
    • Granted, there are ways to bypass this. The shared name Rimuru and Veldora possess does not increase power, but instead is considered 'Equal Status Naming' which has an absurd impact on their growth potential. Rimuru's growth potential rivals that of the true dragons, and even Veldora benefits due to the fact that it affects skill growth as well. He could not have recieved Faust if not for Raphiel being able to boost his processing power through the shared name.
  • Stupid Sexy Flanders: Rimuru resents Souei's good looks, compounded by the speed at which he picks up extra skills. He has similar feelings about Benimaru and his Clueless Chick Magnet status. Ironically, Rimuru himself tends to inspire this in others.
  • Stunned Silence:
    • All the Lizardmen and Rimuru have this when Gobta defeats their leader Gabiru in a single kick. The lizardmen can't believe Gabiru was defeated so quickly, while Rimuru can't believe Gobta actually won.
    • Later, Souei slaughters the orcs in the caves of the Lizardmen so impressively and elegantly that Gabiru's sister is gawking in shock. Her father (the chieftain) and his attendants have the same reaction when Souei puts the last orc attempting to ambush them into a You Are Already Dead situation with razor wire, causing her to hang a lampshade on this trope.
  • Summon Everyman Hero: What the Otherworlders known as "Summons" effectively are, and the key difference from "Reincarnators" who end up in this world at random (usually via death and New Life in Another World Bonus). In theory, it's supposed to be a ritual meant to summon someone with the potential to become a Hero, blessed with incredible powers and skills that will be strong enough to someday challenge even the might of the strongest Demon Lords. In practice, it's been abused by many kingdoms who want the advantage of summoned Heroes with enhanced abilities and powerful Skills gained from crossing over to this world (or even just knowledge of their original world that could be put to military use) to serve as a bolstering force for their military might, and the most unscrupulous ones can carve special runes into the Summons' souls that bind their loyalties to their summoners on threat of death (and they're very much aware of this). And the Summoned doesn't exactly get a choice in the matter or even the chance to refuse, plucked from their old lives at any moment. The process is especially bad when children are involved, as they often don't develop the special skills needed to channel their large reserves of acquired magicules, and will usually die in a few years' time without stabilization from bonding with an elemental spirit. Rimuru truly thinks it's a horrible thing from the first moment he learns about it from Veldora, and once he starts getting influence through Tempest's economic and political power starts advocating for cracking down on Summons.
  • Super Soldier:
    • The Otherworlders are often sought after by various human kingdoms to serve as this. In this world, humans on average lack access to magic or skills, and in order to harness it one must either be born with the aptitude or risk one's life living in Magicule-rich environments in order to passively absorb them and gain the ability to wield them as high levels of environmental Magicules are toxic to life that isn't adapted to it. Otherworlders, on the other hand, acquire a massive amount of magicules from the process of crossing the dimensional plane to this world and have plenty of natural talent at harnessing magic and Skills as a result. "Summons" are often the result of attempting this, but not every Otherworlder develops the combat Skills (or even possesses the fighting mindset) wanted. Plus, child Otherworlders often don't develop the Skills to channel their Magicule supplies at all, and as a result their underdeveloped bodies can't handle their power and they die young.
    • The Holy Empire of Ruberios and the Western Saints Church has their paladins, considered the elite of their military. Each one is trained rigorously to master the combat arts, given high-tier weaponry and equipment, and are often trained in various magics such as Elemental, Summons, and/or Holy depending on their strengths. Even the average paladin is on record as being called worth 1000 normal human soldiers. The strongest paladins are ranked among the Ten Great Saints, each being at least an Enlightened/Sage, and their leader is Hinata Sakaguchi, a Saint who mastered all the combat arts and magics taught to her, wields Legendary-class weapons and armaments that allow her to temporarily stand up against True Demon Lord-level threats, and is considered by almost everyone who knows of her as the strongest human outside of the Eastern Empire.
    • The Eastern Empire boasts a total military strength of 2.1 million soldiers, which quantity-wise is by far the largest army in the world. As this is a world where Humans Are Average and monsters capable of destroying entire towns or single-handedly slaughter an army of normal humans are frightenly commonplace, they've also taken the time to shore up their troops quality-wise.
      • The Armored Division, the main division of the army, has subjected its members to magical modifications that allow them to survive a full week without eating or drinking alongside increasing their physical parameters. They're also equipped with the latest of Otherworlder technology, including firearms, tanks, and airships.
      • The Magic Beasts Division has utilized and weaponized DNA analysis technology to create and breed powerful Demonic Beasts that are ridden by warriors carefully screened and trained for the job. They've also developed a special secret drug that would in theory allow the rider and beast to perform a Fusion Dance to become a Monster Knight of even greater power, but the potential risks of death, insanity, and/or permanent monster transformation mean it's only meant as a last resort.
      • The Composite Division are technically the Rag Tag Bunch Of Misfits of the army, where the fighters too uncontrollable were placed. The reason they're so "uncontrollable" is because most of them are Otherworlders blessed with unique sets of skills and physical/magical abilities that makes it too awkward to organize them as a proper disciplined military force. This is also the place where human experimentation to produce more powerful soldiers was carried out, resulting in the creation of unique "human weapons" that remained under the banner.
      • And finally there's the Imperial Guard, the 100 chosen warriors of the The Emperor. Together, they're considered worth the other three corps combined, as each fighter is at least the level of an Enlightened/Sage and equipped with Legendary-class equipment (which according to Rimuru, comparing such a weapon to a "normal" weapon is like "bringing a machinegun to a sword fight"). The single digits are even stronger, having all the advantages of the double digits alongside a blessing from the Emperor that gives them a pseudo-Ultimate Skill, making them borderline Reality Warpers. The top six are at the level of Saints and wielding the even stronger Mythical/God-class equipment.
    • Finally we get to Tempest and The Black Numbers. Each one of the 711 is a powerful demon, hand-picked by Diablo himself, and granted special artificial bodies tailor-made by Rimuru and Ramiris to serve as ideal hosts. While there are individuals in Tempest that are stronger, they are the strongest unifed unit in Tempest, and their commanders are four of the seven Colored Primordial Demons, the same kind of demon that Guy Crimson is.
  • Supernatural Sensitivity: All monsters have Magic Sense, which detects nearby sources of magic, gauges Power Levels in individuals, and can be used to communicate telepathically.
  • Surprisingly Realistic Outcome: Humans (even most evolved humans) need air to breath, and this has been exploited twice. The first was with one of the traps in the labyrinth, sealing off the room in a way no air would get in or out, meaning setting a campfire could asphyxiate you. This was also used by Guy Crimson against Yukki, since Anti-Skill has no effect on non-magical fire, meaning Guy burned up all Yuuki's air and he would have suffocated if he didn't realize what was happening and deal with the fire. Yuuki has to outright forcibly evolve his body to a fully-matured Saint, removing his human limits in order to remove that method of attack (even if the fight still goes against him).
  • Suspiciously Specific Denial: Veldora certainly doesn't find the heroine who sealed him away attractive, nope. He doesn't think she has lovely hair or that her pale skin is lovely or that she has a personality that he likes.
  • Takes One to Kill One: This logic goes behind the powers of the Ultimate Skills, with few exceptions. According to Guy Crimson, when musing over Clayman "apparently" mind-controlling Milim, only another Ultimate Skill can hope to overpower an Ultimate Skill, and lower-ranked skills simply didn't work on those who possess Ultimate Skills. So if Milim is being "controlled", it's only because she's Not Brainwashed and just playing along for her own amusement.
  • The Thing That Goes "Doink": Rimuru's hot spring bathhouse features a shishi-odoshi for that touch of traditional Japan.
  • Title Drop: At the very end of the web novel, Satoru Mikami, saved from death by the reality-defying power of Rimuru, free to live out his life safe of any paradoxes, and carrying at least some of knowledge/memory of his other self, decides with his junior Tamura's encouragement to tell him all about "that time I got reincarnated as a slime".
  • Took a Level in Badass: If a demon/monster is named by a strong individual, he/she gains more power.
  • War Arc: All over the place, though technically several of them bleed into each other.
    • The first proper one would be the fight against the Orc Disaster, as it involves Rimuru forming alliances with the various races of the Jura Forest to combat the vast 200,000-strong army.
    • The Falmuth Invasion Arc, as it has Tempest going to "war" with the Kingdom of Falmuth's army, though in practice it was closer to Falmuth's unprovoked sneak attack on Tempest followed by Tempest's swift retribution.
    • The Walpurgis Banquet, which is essentially a follow-up to the Falmuth arc and consists of Tempest and Yuurazania fighting Clayman's army and (relcutant) allies in Milim's Dragon Faithful, the simultaneous assault on Clayman's castle, and the clash between Rimuru and Clayman themselves alongside personal subordinates at the banquet itself.
    • The Eastern Empire War Arc involves Tempest clashing against the might of the Eastern Empire.
    • The Tenma Great War Arc, which the Eastern Empire War could be seen as the prelude to, is the Grand Finale where Tempest and their allies across the world fight the true Big Bad and The Armies of Heaven.
  • Wham Episode:
    • Episode 8, where Shizu dies, despite being set up as a Rimuru's partner.
    • Episodes 31 and 32. Due to being delayed by the hero Hinata, Rimuru arrives back home to find that while he was gone, the Kingdom of Falmuth had orchestrated a massacre which killed hundreds of innocent civilians and declared war upon Tempest under the casus belli of "eradicating the evil monsters". And among the causalities is Shion. Before Rimuru has the chance to absorb the corpse to put them to rest though, Cabal's group arrives and Ellen reveals that there might be a way to resurrect the fallen, but it would require that Rimuru become a True Demon Lord. The process would require at least ten thousand souls to fuel the ascension, and Falmuth's invading army just so happens to have twice that amount...
    • Episode 47 and 48. Milim reveals she was always Pretend to Be Brainwashed and never under Clayman's control, and that Frey and the supposed-dead Carrion were conspiring with her. Clayman achieves his Awakening to True Demon Lord level, but is unable to defeat Rimuru and is ultimately killed. Rimuru takes his place at the seat of the Demon Lords, now known as the Octogram with Frey and Carrion stepping down, and Demon Lord Roy is revealed to simply be a Puppet King for the actual Demon Lord Luminous Valentine. Finally, Clayman's comrade Laplace reveals he's actually much stronger than the Demon Lord when he ruthlessly and swiftly kills Roy after the vampire mocks Clayman's end to his face, showing Clayman is far from the biggest threat still facing Rimuru.
  • What Kind of Lame Power Is Heart, Anyway?: Otherworlders get powerful skills based on their desires when entering the world. For Satoru though, he was dying as he was being reincarnated into Rimuru, so his thoughts and desires are a jumbled mess of thoughts like "my god it hurts" and "I can't believe I'm dying a virgin", which the world interprets in weird ways, thus resulting in the skills he gets and the form that he takes. And as the Otherworlders summoned by Farmus prove, the kind of people who get powerful combat skills aren't necessarily the good kind.
  • The Worf Effect:
    • Characters are often compared to a vague 'Demon Lord' or 'Awakened/True Demon Lord' level and for mooks it's always the vague A rank or above A rank metric. This doesn't serve as very good hype since one of the first demon lords seen, Clayman, goes down like a complete chump since Rimuru has already reached that level of power when he fought him while "True Demon Lord" can range from small fry like Ramiris to literal gods depending on how much power they gained before their ascension and how much they kept building it up afterwards.
    • This actually pointed out in the light novel that anyone who reaches a certain level of power can proclaim themselves a Demon Lord, but in order to be officially recognized as such they need the backing of two existing Lords or be ruthlessly crushed by the established ones. So many such self-proclaimed Lords have come into existence that at least one human kingdom doesn't even consider it a big deal. Milim herself notes Rimuru had already surpassed the minimum power requirement to become a Demon Lord just days after fighting and absorbing the Orc Disaster. A similar case occurs with the "Ten Great Demon Lords" as only four of them were "True" Demon Lords while most of them were only self-proclaimed Demon Lords of varying degrees of strength. Carrion and Frey even stepped down after Rimuru defeated Clayman since they realized they couldn't match up to the rest.
  • World of Technicolor Hair: A more justifiably limited example, where humans and human-adjacent races (dwarves and elves) only have hair colors common in real life, while completely inhuman races like shapeshifted slimes, oni, goblins, demons, and more commonly possess a wide range of hair colors, such as blue-haired Rimuru, lavender-haired goblins, green-haired dryads and witch Myulan, and demon-kind possessing hair matching the Color Motif of their associated progenitor, of which four (Testarossa/White, Ultima/Purple, Rain/Blue, and Misery/Green) are not normal in humans compared to the other three (Guy/Red, Diablo/Black, and Carrera/Yellow).
  • Worthless Yellow Rocks: In the eight episode of Slime Diaries, Rimuru is excited that the others found matsutake mushrooms, which are quite rare in Japan. However, Rigur and Benimaru explain that the mushrooms are quite common in the Jura Forest, and they just happened to collect some while foraging.
  • Your Days Are Numbered: Once a Summon (a person yanked from the different world by magic) fails to develop a skill that allows them to deal with the enormous level of magicules acquired during the ritual — which is a common, and even a normal occurencetheir bodies fail within several years. This is especially the case for anyone summoned when still immature, i.e. children which is why Leon bound Ifrit to Shizu, as that would prevent the phenomenon from occuring for decades.

 
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Alternative Title(s): Tensei Shitara Slime Datta Ken, That Time I Got Reincarnated As A Slime

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Demon vs Spirit

The demon who'll be named Diablo points out the tactical advantage spirits has against demons while showing that he's so powerful that it doesn't matter.

How well does it match the trope?

5 (8 votes)

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