Izuku will be transported to another world during the USJ attack. This world is entirely made up so it's not based off of anything. The time in said world works differently to the one he came from. Izuku whilst staying in this world, practises and trains over and over until he feels like he'll pass out. He'll be eating animals inhabiting the place as well as eating demons. You see, in this world, Demons do indeed exist and by consuming them you can gain strength. Izuku at first just thought of the demons as animals and hunted ones he thought were weaker than others which led to his strength increasing at a fast pace and eventually he climbed the ranks and eventually ate Demons that were strong enough to destroy planets. Izuku's irises to change to blood red as well as his teeth sharpening. Izuku at the time he returns back to his own world could use 100% of One for All but even in his base strength he's able to beat most of the hero's but would have trouble against the top 5. (I don't own My Hero Academia, obviously)
3 parts