(MHA #3)
Unrelated to All for One at all, in one of AM earlier clashes with another SuperVillain(random multiverse 15m. of fame first is Castiel from 'Supernatural').
He gets cut/stabbed with a knife that has a proto-trigger(the quirk boosting drug) and mysterious chemical on it, he survives and defeats his opponent soon after but has a delayed reaction with One for All later, and so his quirk can no longer be transferred.
Over a year or two the past bearers start talking to AM(he does not get access to their abilities)at first he is caught between denial, worry of madness, and horrific soul crushing hope(to be able to speak/try to apologize to his mentor for his weakness/Nana Shimura).
She then pulls him in and lays a beat down on him for being thick and trying to shoulder the weight of her folly's, before pinning him and embarrassing him in front of the past bearers before he cries uncle and they settle in for some serious talks.