Quirks manifest themselves usually at age 4. Sometimes, they appear under extreme duress or strong power of will. Izuku Midoriya suddenly finds out that he is the latter...after getting One for All. And its abilities are confusing to both his friends and himself. How does it work?

What if Izuku unknowingly possessed a "sentient" Quirk like Tokoyami's Dark Shadow? Enter Midoriya Izuku, a young boy thought to be Quirkless who subconsciously controls the number one vigilante in Japan; an entity powerful enough to rival even the strongest villains. There's only one small, tiny problem: the entity thinks of him as a big brother. Good luck, Izuku-nii-chan!

Bakugou Katsuki is selected by All Might as his new successor while Izuku continues his dreary existence as a Quirkless aiming to become a hero. After one day finding out that his childhood bully was gaining everything Izuku ever wanted, he finally crosses the line and takes matters into his own hands. Quirk!Izuku, SplitPersonalities!Izuku.

(Spider-Man Crossover) While being created, part of the Noumu formula is used on a spider and "kills" it. Unfortunately, Izuku is on the wrong end of its fangs at the worst of times. With an extra "Quirk" at his disposal, follow Izuku Midoriya at UA High School trying to deal with villains, vigilante work, girls and... his own powers? (OP Izuku, Izuku X Harem)(DISCONTINUED)

Izuku Midoriya, previously thought to be quirkless, develops a quirk that is among the most powerful in the world. With this quirk he might just achieve his dream of being the greatest hero while finding something else along the way. Quirk!Izuku. OP!Izuku. Also OOC. And IzukuxMomo, because why not?