Ace Attorney Izuku Midoriya AU
I've been getting back into Ace Attorney recently and had this random idea. An AU where All Might never drops the Sludge Villain and thus Izuku never gets the opportunity to prove himself to him and gives up on being a hero like he was going to do in canon before All Might got to him.
And, eventually (maybe a few years later down the line, but could be at any point really), he gets pinned with a murder somehow and it's up to Mia (or someone else) to defend him (and they're Quirkless, too). Izuku gets inspired by them and realizes that even if he can't become a hero due to his lack of Quirk, he can still save others this way and decides to become a Defense Attorney. Cases would probably be pretty interesting, due to the introduction of Quirks.
Update:
I thought a little more about potential cases for this AU and came up with one I kind of liked:
This would probably be the final case. But a case where All Might, as Yagi Toshinori, is accused. Izuku, being one of the few who knows his real identity, realizes how potentially catastrophic this could be. If he's found guilty, there will be no symbol of peace to protect people, as at this point in this story he hasn't found the right person to give his Quirk to so it would end with him. And not only that, if he's found guilty it would inevitably be revealed who he is at some point, and would cause chaos when the world is faced with the "fact" that their number one hero is a murderer. And his "crime" in conjunction with being locked up and unable to keep going as a hero or give his Quirk to someone else would probably cause a villain uprising. A lot would be at stake in this scenario, so it would be fitting for a final case.