It's Midoriya's first day at Shiketsu and when the principal brings him into his homeroom to introduce him, there's something else to announce as well.
"As you know," he says, "we've been looking for another heroics teacher to help keep up with you for a while. I am, uh, very pleased to tell you --" and even more confused, his expression says -- "that we just hired on All Might as your secondary heroics teacher. It was very sudden."
The students spend the day getting used to this; it's easier when they go to Heroics that afternoon and realize that the skeleton-looking man who's been sitting in the back of every class is All Might. It's even easier when they see All Might's lanky figure shuffling note cards around when he thinks they're all paying attention to Ms. Joke. It doesn't take for the students to come to the logical conclusion about All Might's relationship with the transfer student, Midoriya, but most of them are happy to keep quiet for now.
That night, Eri wakes up Aizawa in the middle of the night. All she will tell him is that she dreamed about a tall man with white hair who needed her help; the description sounds familiar enough to give Aizawa chills, but he pushes it aside to help her get back to sleep.
On Midoriya's second day of school at Shiketsu, the principal comes into homeroom again, this time looking much paler.
"I know you're still getting used to All Might," he says, "but last night your History of Heroics teacher quit. Unexpectedly."
The classroom erupts in a flurry of concern.
"Ah, but, we've already found her replacement! Mr. Midoriya was ever-so-eager to come help out and spend more time with his son."
Midoriya sits up straight, startled. All Might, in the back, coughs up blood in surprise. The students simmer in confusion.
A tall, white-haired, well-dressed man walks through the door, looking like the cat that got the canary.
"I'm quite pleased for the opportunity to help mold the minds of tomorrow, and to finally spend some time with my beloved-- YOU?" He exclaims suddenly, noticing All Might with a look of pure horror.
"YOU?" All Might shouts back, just as horrified.
"DAD?" Izuku cries, looking back and forth between them in distress.
Dads? the students wonder. Dads, the students decide, already wondering how no one had ever heard of All Might's ex-husband who clearly provided the genetic material for their child.
The principal sighed. This'll be one long semester.