Izuku isn't who he thinks he is, and his Father too. He's always gotten told his Dad was doing work overseas, until his last year of Middle School, and his Mother said he died, but that was just a coverup.
Inko Midoriya always knew Izuku would get in U.A, and that he has a quirk. Of course, its his Father's too, but she always put something in his clothes to make him seem normal. She had asked the doctor to say he's quirkless, to keep it even more hidden, since he has his fathers quirk.
Unknown to Izuku, his Dad is the one and only; Present Mic, or, Hizashi Yamada, who had become a Father at 16. He had been told he took his grandfather's last name, to cover up the fact Izuku is Hizashi's kid, but that was a lie, he took Yamada anyways. Hizashi never even knew until a school wide Blood Test went in order, to make sure nobody was a villain in disguise.
To say both were shocked was an understatement. Want to know what they did? Read to find out.
NOTE: In this story, Inko is gonna be 35, 4 years older than Present Mic