MHA Story And Quirk Ideas

Quirk: Tense

Izuku's quirk is Tense. It's an Emitter/Mutation type that lets Izuku basically become the incarnation of immovable object and unstoppable force combined. When Izuku tenses his muscles, they link together so tightly that not even the full force of All Might can harm him. The only thing that can hurt Izuku when he tenses his muscles are Quirks that work from the inside out. Forces from the outside in will never work. [So quirks like Overhaul and Decay]

The Mutant aspect comes from the way his muscles are structured. See, they're built in a way that allows him to move as fluidly as if he wasn't tensing them at all. They're also built so that when he makes more muscle, it condenses in such a way that he can always make more. Theoretically that leads to the ability to make muscle infinitely, meaning the more muscles he makes the stronger he'll be physically. However that ability comes with a massive downside. Quirks that drain strength don't just take stamina. For him, they literally start to decompact his muscles, making him heavier and more cumbersome until they deactivate their quirk, at which point they slowly start to recompact themselves. To be back to normal, add 1 minute for each pound of muscle. This weakness can be trained to recompact faster through repeated exposure, however it will never go away. Peak speed of recompaction is 30 seconds ad during this time he cannot Tense them.

In order to promote musculature gain this quirk makes it easier to break muscles when exercising, but in exchange gives his muscle fibers a regeneration aspect. This leads to a weakness in fights where he has to move around a lot, as lactic acid builds up easier for him than for normal people. While this can't be trained away, he can be trained to ignore it, as the lactic acid makes it seem like his muscles aren't OK, when in actuality they're completly fine.