Luna, the deity of anarchy and revolution, desires to slay the chosen champion of her sister. However, due to their very nature, Luna would be too bored to follow a straightforward plan and wants her pawns for the gambit to attempt rebellion against her.
To that end, she copies the minds and personalities of the people of a specific world and implants those into available souls, and picks two of them to be the joint minds of a Dungeon Core. Now Izuku and Tomura must work together to build a great dungeon after being thrown into the deep end by Luna.
The Core Problem
is a My Hero Academia fanfiction created by Mirrond.
This fanfic contains examples of:
- Actually Pretty Funny: Izuku admits that Tomura calling All for One's level of edgelord pizza-cutter level, as in, all edge and no point, to be an actually good insult.
- Adaptational Superpower Change: All Quirks are lost upon the transfer to the new world.
- Adaptation Personality Change: After being forced into a fantasy world, Izuku turns towards being very snarky with Tomura as a coping mechanism.
- Adaptation Relationship Overhaul: Due to being forcefully taken from their world and placed in the new one, the characters previous conflicts in the canon of My Hero Academia are rendered largely meaningless and most see it as a fresh start.
- The Assimilator: A dungeon gains more options by absorbing things within its domain.
- Bait-and-Switch: Tomura tells Izuku that his words reached his heart and he will strive to be better. It seems like he will be a better person before he clarifies he will be a better villain.
- Big "NO!": Monoma shouts a big no after learning that after being isekai'd, the class rivalries don't matter anymore.
- Bizarre Alien Biology: Hamadryads bleed tree sap instead of blood.
- But for Me, It Was Tuesday: Izuku is annoyed Tomura doesn't remember his name even though he threatened to kill him. Tomura responds that he threatens to kill a lot of people, and that incident with Izuku was not that special to him.
- Clone Angst: One not-insignificant point of contention the characters have with what Luna did is that they are the copies of the original people they were. Some are more distraught by this fact than others.
- Dark and Troubled Past: Invoked by All for One. He manipulated the circumstances of Tomura's Quirk Awakening to destroy his home and family and leave Tomura wondering the streets until All for One "finds" him. Tomura did not realise the manipulation until Izuku points out that it is nigh-impossible for the authorities and society in general to randomly drop the ball that hard for him.
- Death Is Cheap: When a Dungeon Servant dies, it's not that big a deal. The Dungeon can just revive them if they recover the souls fast enough and have the mana levels to spare. This allows Tomura to tell Himiko to die tactically so that the people after Ekana will assume Ekana's dead without further investigating.
- Dem Bones: The Breathless Tide have a category of undead called Skeleton, which are just walking skeletons.
- Desperately Craves Affection: Izuku and Tomura quickly realize that if Himiko's feeling lazy, a quick way to get her off her ass and do some work is to tell her either Izuku and/or Ochako would appreciate the effort.
- Didn't Think This Through: Himiko throws her torch at the hamadryad while fighting her. While it helps and she ultimately kills her opponent, it also started a small fire. Thankfully, it is put out before it could grow out of control.
- Discard and Draw: Izuku and Tomura have the ability to switch skills around for their subordinates. They can't do this freely though as the more skills they have, the higher the mana they need to function.
- Distracted by My Own Sexy: Himiko is briefly distracted by the fact Tomura made her breasts bigger when she takes off her clothes.
- Drama-Preserving Handicap: If mana-levels allow it, a dungeon can freely change the layout of a floor, unless there are outside forces present. This means no making new traps for active hostiles to make things easier.
- Dungeon-Based Economy: It is possible for societies to make deals with intelligent enough dungeons for the society to obtain goods from the dungeon in exchange for the dungeon taking the occasional casualty and new goods to produce. This doesn't unbalance the economy though since more valuable goods require higher mana levels to produce, which necessitates braving more dangers to get them.
- A Dungeon Is You: Izuku and Tomura are made the joint consciousness of a dungeon's core, and have to work together to get things done.
- Eating the Eye Candy: Himiko isn't shy about appreciating Ochako's look both in general and when she's in action.
- Enemy Mine: Enforced. The hero students and the League of Villains are forced by Luna to work together to survive. Especially Izuku and Tomura since as the joint consciousness of the Astral Core, anything they do with the dungeon requires them both to agree.
- Fan Disservice: Whenever Izuku feels Tomura went too far, he gets payback by showing him images of naked All for One and Dabi. Worse, they are shown as catboys. Izuku also uses other men in his torment of Tomura.
- God of Evil: Luna outright calls herself a god of evil, and between her domain of anarchy and her actions of dumping people into a life-and-death situation in Chapter 1, she lives up to her claim.
- Going Native: Izuku is worried that he and his companions are adapting too quickly to the new world, from Ochako converting to the faith of one of the local gods to the hero students adapting their morality to the lower standards for good.
- Good News, Bad News: Tomura tells Izuku the good news that the latter's slime trap worked, before giving the bad news that the intended non-lethality feature didn't work properly and Itar, the person who fell for it, is dead.
- Healing Checkpoint: Node Rooms contain secondary dungeon cores that allows skilled enough mages to tap into the mana flow of the dungeon, allowing them to use the dungeon's own mana to cast spells.
- Hoist by His Own Petard: It doesn't come to fruition, but Tomura admits to Izuku he was already considering killing All for One for being annoying. On further prompting, he also tells Izuku that All for One taught him to destroy everything he finds annoying and says his mentor shouldn't be surprised by that, which Izuku concedes to.
- I Have Your Wife: Luna forces Izuku to comply with her orders to kill the chosen of her sister by threatening eternal torment of his loved ones.
- Info Dump:
- The fox-beastkin elder tells her companion Uzar a lot about what she heard about how dungeons work in Chapter 7. This is useful for Izuku and Tomura since they manage to hear the entire explanation and put up a convincing act to outsiders.
- Aeonia gives a long explanation on the cosmology and theology of the world in Chapter 17.
- Chapter 20 provides descriptions for several different spells.
- Luna explains how the Laws mechanic work for Dungeons in Chapter 20.
- Insistent Terminology: When Tomura realizes them just taking things from the burial site they found counts as grave-robbing, Izuku insists on calling it "archeology". Momo eventually disabuses him of this notion. She says that for something to count as archeology, it has to be done for the purpose of advancing knowledge and items taken have to be placed in a museum or otherwise used in study. What they are doing it taking things for personal benefits.
- It Only Works Once: Luna's failsafe to protect Izuku's and Tomura's Astral Core from certain doom is explicitly a one time thing only.
- It's Personal: Tomura's hatred of All for One becomes personal when Izuku makes him realise All for One manipulated the circumstances that led to his beloved pet dog Mon-chan dying.
- Let Me Get This Straight...: In Chapter 19, Yaoyorozu sums up the story premise and events thus far to see if she understands everything.
- Love Makes You Crazy: Himiko is perfectly happy to die on Izuku's orders because she could get him to call her by her first name after she gets resurrected. Izuku lampshades this to Tomura who tells him he long stopped expecting logic from her.
- Meaningful Name: The dungeon group notices that the names of the High Gods are derived from Latin. Saevius for example is derived from the Latin word for 'cruel', 'barbarous' or 'savage'. Luna is a moon-based name and she is a moon goddess. Same with Sol the sun goddess.
- Metaphorically True: Not wanting to outright lie to Himiko but also not wanting to alienate her, Izuku tells her that Ochako is thinking warm thoughts about her. Tomura is quick to clarify that it means Ochako hopes she burns in hell.
- Mission from God: Luna the goddess of anarchy and revolution orders Izuku and Tomura to kill the chosen of her sister, after which she will leave them alone. Izuku has reservations due to Luna being a self-proclaimed evil god.
- Mr. Exposition: Aeonia is the first being the dungeon crew encounters that they could ask things about the world, and she more than delivers with in-dept explanations.
- Names to Run Away from Really Fast: The trope is name-dropped when Tomura learns that one of the old names for Rampant Bloom is Locust-That-Walks. Izuku agrees with his sentiments.
- Necessary Drawback: Izuku and Tomura can't just give their subordinates as many abilities as possible. More skills requires more mana levels for their subordinates to function, so if they give too much, they can't do things outside of the dungeon so easily.
- New Life in Another World Bonus: Invoked. Luna read up more of the isekai genre and realizes she didn't give Izuku and Tomura special cheats isekai protagonists usually get, and so, gives them some in Chapter 20. Their bonuses are as follows:
- They now have the ability to cash in divine favour for gifts from the various deities. This ranges from summoning shard spirits and daemons from their domains, to having one entire level modelled after a single spiritual world.
- Izuku and Tomura are given additional flexibility in managing dungeon servants not available to other Dungeons. There are some limits for balancing reasons, but the options are as follows:
- Normally, souls contracted to Dungeons can have skills inserted into them by the dungeon, but lose them when they leave. Luna makes it so that with Izuku and Tomura, they have the option of keeping those skills. However, they cannot rejoin the dungeon. The decision to leave will be permanent in that case.
- The souls made up of the My Hero Academia characters also gain the ability for independent growth and give the dungeon access to new skills that way, but, they must decide on a permanent body. No body switching is allowed for any individual that makes this choice.
- The souls made up of the My Hero Academia also have the option of overriding the soul of a daemon they captured as opposed to getting to agree to serve them. This choice is also a permanent one, and Luna is giddy to see the results of that.
- Nightmare Retardant: In-Universe. The more Izuku learns of and deals with the eccentricities of the League of Villains, the more their previously intimidating image gets broken.
- Pervert Revenge Mode: When Tomura shows Izuku a preview with an image of a naked Ochako, then alters it so her breasts becomes bigger, Izuku retaliates on Ochako's behalf by showing Tomura a naked Dabi.
- Pocket Dimension: Pass the first level of a Dungeon, each separate level is technically its own separate space. This allows Izuku and Tomura to move the passageway between levels on one floor without affecting other floors.
- Platonic Life-Partners: Discussed. Tomura thinks best friends of compatible orientations and genders are just couples in denials in defiance of this trope.
- Rule of Three: In Chapter 19, thrice Tomura tries to rebuke Momo's assertion that the League of Villains have a poor track record, and thrice Izuku points out the issue with each argument he makes.
- Seeing Through Another's Eyes: Dungeons have the ability to see through the eyes of their servants, as well as more generally experience the world through their other senses.
- Selective Obliviousness: One huge blind spot for Izuku is him giving Bakugou undeserved admiration. Even Tomura can see Bakugou's flaws, but Izuku refuses to see them.
- Shameless Fanservice Girl: Himiko has zero qualms about using her body to get a reaction out of Izuku.
- She Is Not My Girlfriend: Izuku denies Ochako and Himiko are his girlfriends to Tomura in Chapter 16. Tomura just grumbles at him.
- Shout-Out:
- Tomura references Dark Souls, specifically the Sen's Fortress location, as the inspiration for his boulder trap level.
- When Yaoyorozu and Kirishima first manifest, they point to each other in a way that reminds Tomura of the famous Spider Man meme.
- Superhuman Trafficking: The Astral Core of a dungeon is extremely valuable, but the only ethical source of it is from authorized executions of homicidal ones. Demand far outstrips the legal supply and dungeons that don't deserve that fate may find themselves facing people trying to kill them and take their core.
- Stalker with a Crush: Ochako succeeds in getting Himiko to downplay this trope by making her understand that respecting boundaries will endear her to Ochako and Izuku better than her simply violating their privacy and personal space.
- Taught by Experience:
- Izuku and Tomura are tossed into the deep end by Luna with minimal aide and guidance in fulfilling the task she gave them, and so have to learn almost everything about how the dungeon and the world in general works through experimentation and experience.
- The fox-beastkin elder admits that she used to be a rash youth alongside the rest of her generation. And then she noticed her fellows dying and learned better, becoming a wiser elder.
- Teeth-Clenched Teamwork: Izuku and Tomura don't like each other, but have no choice but to work together to survive. They do choose to get on each other's nerves though.
- Too Kinky to Torture: To Ochako's consternation, her ability to punish Himiko for various things is severely compromised by the fact that Himiko enjoys being punished by her. Admittedly, an inability to permanently die takes most of the fear out of such things.
- Trapped in Another World: From the perspective of the characters, they were forcibly taken from their world and have no hope of ever going back.
- Why Didn't I Think of That?: Izuku calls out Tomura for his stupidity as a supervillain leader by pointing out that since Himiko was able to turn into him, they had the perfect way to frame him of serious crimes and ruin Izuku's hero career. Tomura for his part is shocked he himself did not think of such a brilliant plan.
