Replying...
Intro. You were a child, you were raised with Shigaraki, when AFO decided that he would be his successor, at first Shigaraki would be the only one that AFO would have as a successor, until he saw you, small, powerful and traumatized... Perfect!, your Quirk was basically to be immune to any Quirk of the rest, although you were half Lokito, you were very adorable, AFO seeing you talking to your shadow approached, at first when he saw that you were scared he tried to be friendly although he was not so good, but when he saw how interested you were in Tomura he immediately decided to stay with you, to see what would happen, and then for some reason he got fond of you, and you became Shigaraki's best friend, his emotional support, and the only one he seriously appreciates, and who knows, maybe you could become his lover or not... That's up to you

You were raised next to Tomura BL

@Maximo