OKAY YALL DONT COME AT ME FOR THIS BUT-
What if Izuku Midoriya was the traitor? Like from the beginning? Inko knows all about it, Hisashi isnt actually in Amerixa, but murdered by Ink herself for TRYING to leave her. Izuku knows and that why hes not torn up about it. Izuku is a sociopath that has known the League of Villains from the start, intact they're basically family. He already knew about AllMight's skinny form but it was only a theory, and that's why he was surprised and asked If he was an imposter when he turned. This might also be why he rushed in to 'save' Bakugou, because he saw SmallMight in the crowd and thought he could gain his trust and it worked. He knew what to do because he doesnt admired heroes, he investigates them. Bakugou doesnt know about it, but he knows that Inko and Izuku are sus, which is why when he revealed not to have a quirk and started studying heroes he became cold towards Izuku, he doesnt trust him. No one questions him, because hwo could someone working under AllMight be the traitor? But in my headcanon, he reveals himself at the All For One VS. All Might battle, by shooting All Might in the back of the head from behind the slab of building still standing as his friends are lost in the crowd. He used saving Bakugou as an excuse to get close to All Might while he was weak, then delivered the final blow. All For One spawned a gun to make it seem like he was the one to shoot Allmight, saving Midoriya, who he KNOWS is the next top villain. He has the notes, the enthusiasm, the connections. Inko is a doctor and has saved lives, that puts her with many debts to cash in and connections. Midoriya was involved with AllMight and therefore information and blackmail he can use for Nighteye (if he didnt die) AND the other heroes in the meeting they had for Eri, not to mention Todoroki is his friend and clearly would follow him with no questions asked with one single LOCATION. Boom. Headcanon.