Why is All Might here
Just after Hisashi had gotten rid of the hero brat knocking came from the door. WHYYYYYYY. He just wants to spend time with his cute little green bean, why must people keep interrupting them. Hisashi stood to his full height which was a good almost eight feet tall and quite intimidating ( actually it's kind of a miracle how short Izuku turned out considering his dad's height ). He walked over to the door and opened it with a scowl on his face.
There standing in his entryway was fucking All Might. Why exactly was Japan's number one hero interrupting Hisashi's time with his beloved son. "What do you want?" ok maybe that was kind of rude, but he just wants to stop socializing for a little while today. You don't get to be king of the underworld without being a master of avoiding people, and as an introvert All For One had absolutely no problem with that. The only people who don't drain his social battery are his family, and All Might certainly does not fit on that list.
"I am here to speak with young Midoriya's mother about official UA business. Is she here?" He's looking for Inko! Why didn't he mention Izuku's father! Sure he doesn't live at home most of the time but Hisashi should still on all of Izuku's paperwork.
"I am Izuku's dad, anything you need to discuss with Inko you can say to me." He stood up a bit straighter and was quite pleased when he saw All Might pail a bit at Hisashi being Izuku's father. Seems like even in his civilian persona he still has the power to strike fear into the hearts of even the most powerful people. Well except for Inko, that woman could be terrifying when she wanted to be. When informed that Hisashi was king of the underworld she just told him that she had known since their third date ( Apparently her parents were retired supervillains who taught her a few things ). That may have been one of the most horrifying experiences of his life, and it was at that moment that he knew that Inko would be the one he would marry.
"Well UA is implementing a dorm system for all of its students in light of the recent attacks by the League of Villains." THIS HERO SCHOOL WANTS TO TAKE IZUKU AWAY FROM HOME. ok it'll be fine Hisashi can just pull Izuku from UA, homeschool and train him privately for the hero exam. You don't technically need to go to hero school to enter the exam. He's heard of some vigilantes becoming full fledged heroes through that method.
But what would Inko think? Hisashi couldn't just take Izu away from all his friends. Unlike Hisashi, his son actually liked socialization. Uhhhh. That means he actually needs to let his Izu live with his classmates. Wait, did that mean he would be sleeping in the same building as his boyfriend? Has he even given Izuku 'the talk' yet.
"So what exactly is the sleeping arrangement for these dorms?" because if there was more than one person in a room Hisashi would do anything in his power to separate Izuku and Shinsou. He would resort to murder if he had to.
"I believe that each student will have their own room with boys and girls on opposite sides of the building." Well at least this buffon had some use.
"Have a tolerable day." and with that All For One shut the door on his mortal enemy's face.
Socialization for the day done. Now he can finally go get some hugs from his green baby.
"Izu come give me a hug." maybe he said that with a bit of a whiny voice, but sue him ok he had an exhausting day. First some of his subordinates formed a rebellion that he had to put down, then he comes home only to find out his beloved son has a boyfriend, then he is forced to interact with one of the people who annoys him the most. On top of all that, Hisashi has been unable to come home for almost three months because of helping Tomura get the League of Villains up and running. So he's a little green bean starved.
"You're not just going to pick me up again like last time are you?" he called from the other room.
"Of course not! What do you take me for Izu?" The most feared villain in Japan and perhaps the world said as he walked over to his son and scooped him up. Even at fifteen Izuku was still significantly shorter than his father and Hishashi took full advantage of this by taking every opportunity to pick him up and carry him around just like he did when Izuku was younger. Izuku giggled every time this happened and just settled into his fathers embrace.
This is where Hishashi was happiest, with his son in his lap. The only thing that could make this better was if his wife was seated next to him like they did when Izuku was a baby.
Ultimately whatever happened in Izuku's life so long as Hishashi got to hold him like this nothing else really mattered.