Sometime after having sex with Mina, Izuku seeks out the progenitor of his quirk, All-for-One. He visits him in prison on the pretext that he’s there to interrogate him. Shigaraki senses his presence immediately.
S: “Midoriya. Your name, was it not?”
M: “I’ve come for answers… All For One.”
S: “You wish for the secrets of your quirk.”
M: “Yes.”
S: “I gave it to my brother, Yoichi. He made it into a mission. And from my predicament, one may deduce his mission was a partial success.”
(PAUSE)
S: “What’s wrong? You expected resistance?”
M: “Yeah…”
S: “I’ve outlived generations, Midoriya. I am immortal, and you are but a distant echo of Toshinori. I lose no advantages by telling you the complete truth.”
M: “I know in my heart you’ll escape some day. But our coming battle is not what I’m here to discuss.”
S: “Yes. Toshinori never told you about his quirk’s fault.”
S: “You never wondered why he was eager to give it up?”
M: “Because of his injuries, that he got while fighting you.”
S: “False.”
M: “What’s my quirk’s fault?”
S: “It renders its wearer completely unattractive to women.”
M: “And how would that work?”
S: “Simple. You’re giving away everything to others. One For All stops working without self-sacrifice.”
M: “I do just fine with girls.”
S: “Women want men who have things. Power, status, resources. And you… selfishness renders you powerless.”
M: “You’re saying Toshinori gave me his quirk, to have a relationship?”
S: “Precisely. And in doing so, he robbed you of that ability.”
M: “That would explain how he was single…”
S: “Despite his popularity, yes. But he no longer is. He has someone.”
M: “And how would you know that?”
S: “….”
M: “Who?”
S: “Search your feelings, Midoriya. You know who it is. ”