Who's Your Daddy?
“If anything,” Shouta huffs, “he’s my son.”
“Oh?” All Might responds in a teasing voice that has just enough edge to it that the students know a fight be brewin’ on the other side of the door. “And how do you figure that, Aizawa-kun?”
“Maybe from the fact that he’s in my homeroom class?” Aizawa challenged, to which a faint tsk could be heard from All Might.
“I gave young Midoriya his power!” All Might challenged.
“Oh, yes, congratulations,” Aizawa drawled on sarcastically. “Just go ahead and pass on an immense, immeasurable power to a literal child and then let him take the biggest exam of his life with little to no explanation because - well,” he scoffed, “if he can do a few community service hours lifting junk off a beach, then obviously breaking all the bones in both his legs and one arm will be a snap!”
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TL;DR: A crackfic where Aizawa and All Might argue about who's got more of a right to be a parent to Midoriya (who's dying of embarrassment in the back corner).