I made an edit to Chapter 4. The next part won't make sense if i didn't.
Traitor Uraraka, Twin, & Dad For One AU.
Uraraka is the youngest daughter of All For One. Her biological mother died during birth leaving her in All For One's hands. He decides to raise her side by side with Tomura to become a villain.
She grows up alongside Tomura. She gets a gravity quirk when she's four (4) & officially begins to train. She lives a double life so she can get in too U.A. to spy on them.
Meanwhile, Inko knows that she's married to All For One, he told her before he proposed to her. She still accepted him after he told her. Later she got pregnant with twins. (Izuku & Izumi) Izumi manifested a combined version of All For One & Inko's quirk (All To One) at the age of three (3). However, Izuku never manifested a quirk. Instead of Inko going to his room & breaking down after Izuku asks her if he can still become a pro hero without a quirk, it's All For One he says yes but he has to work harder in order to do so.
*Skip to Middle School/Junior High*
Goes same as canon, except when Bakugou tells Izuku to 'take a swan dive off the roof', Izumi is there & punches him in the face.
The slime villain attack goes the same way except Izumi is also caught in it.
All Might saves them. Izuku accidentally grabs on to him, so when All Might jumps he takes Izuku with him.
The rooftop & 2nd slime attack goes the same way.
After saving Bakugou from the slime villain, they try to go home. All Might stops them, without realizing Izumi is there. He asks Izuku to be the 9th user of One For All. He accepts because the question came out of the middle of nowhere. All Might then transfers OFA to him & runs away.
Izumi: 'What the f*** just happened?'
Izuku: 'I think I just got a quirk.'
They won't see him again until U.A.. Any who... they go to the entrance exams & meet Uraraka.
TBC