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Our protagonist, Rimuru: slime... and human.
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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.

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.

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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 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.
  • 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.
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  • 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.

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).
  • 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.
  • 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.
  • 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.
  • Awesomeness Is a Force: Downplayed with King Dwargo who is described by Rimuru as 'exuding an aura of raw power'.
  • 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 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.
  • 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.
  • 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".
  • 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.
  • 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.
    • 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.
  • 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.
  • 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.
  • 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.
  • 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 dukes. Lesser demons are reasonably strong, but both they and greaters are basically fodder. Archdemons are rare, powerful monsters and demon dukes are nearly unheard of. The latter are at the same level as demon lords.
  • 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 Bester 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 Leom 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.
  • 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.
    • The Council of the West is one for almost all the human nations west of the Jura Forest, having bandied together to better hold against the encroachment of the Demon Lords and the Eastern Empire while also increasing their own influence in the world.
  • 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.
  • 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.
  • 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.
  • 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 don't use maps or writing and can't pass as much knowledge onto their children so humans are the most advanced civilization.
  • Humans Are Average: Humans appear to be normal humans, only treated differently by 'monsters' since adventurers kill them.
  • 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).
  • 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 he ogres he needs to have children. He only evolves after producing an heir with Momiji.
  • 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.
  • 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.
  • 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 Rimiru'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 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.
  • 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.
  • 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.
  • 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.
  • 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 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 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).
  • 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.
  • Reality Ensues: 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.
  • 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 Rimiru 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 Rimiru'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.
  • 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.
  • 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
  • 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.
    • 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 Kill Them All 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.
  • 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 devil dukes, which are in turn overshadowed by devil lords.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Took a Level in Badass: If a demon/monster is named by a strong individual, he/she gains more power.
  • 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...
  • 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 seven of them were "True" Demon Lords while three of them (Carrion, Frey, and Clayman) were still self-proclaimed ones. The latter two even stepped down after Rimuru defeated Clayman since they realized they couldn't match up to the rest.
  • 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 mana 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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Hellfire Snowclearing

Fire magic. Useful for more than battle.

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5 (2 votes)

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