Aizawa walks in the classroom holding the hand of a very distressed Midoriya; he explains to the class that the boy was hit with an affectionate quirk and that he needs physical affection.
Obviously, the whole class volunteers, because they all have a crush on Midoriya and everyone knows except Midoriya himself.
Aizawa knows this and that's why he doesn't want to leave the boy with anyone, however, because Bakugo has been really good at hiding his true feelings for Midoriya (and he's been trying to make amends with the boy) Aizawa thinks Midoriya will be safe with Bakugo.
As everyone else starts bemoaning (Todoroki makes sure to point out Bakugo doesn't deserve to have Midoriya all for himself) Midoriya runs towards Bakugo's desk, sits on his lap, puts his arms around his neck before sighing happily.
"Thanks for taking care of me, Kacchan!" He says, nuzzling against his cheek.
Aizawa kind of expects an explosion or at least a complaint, but Bakugo pulls Midoriya closer to his chest and keeps writing on his notebook as if nothing happened.
"You're such a needy nerd," he says, almost fondly.
Suddenly, it occurs to Aizawa he might have made a mistake, but decides not to think about it too much.
The bad feeling comes back when it's time to go to the gym and Bakugo hasn't complained even once about having Midoriya wrapped around him, actually it seems like he doesn't want to let go of him.
"Bakugo can't take care of him all day!" Uraraka protests. "At least let us have Midoriya for a while, sensei!"
"NO!" Bakugo moves away, cradling a very happy Midoriya in his arms. "YOU SAID HE WAS MINE!"
"I never said that," Aizawa sighs, feeling tired already. When the others look more than ready to try to steal Midoriya away from him, Aizawa finally admits he made a huge mistake.