@es_kan
He did, but they kept giving him sexual harassment prohibitions (lick a girl's leg, kiss someone), which he wouldn't do even if they were not prohibitions. That's why he kept shouting, "Isn't that illegal anyway?!" or "Why are they giving me prohibitions I won't do?!" I think your mistake is trying to speedread this manga, it isn't coherent or consistent enough to be read as fast as you're reading. Maybe you didn't read it for 2 years, and you forgot the story.
I think the MC knows Mizuha from a Black Bout. He defeated her, and that's why her family disowned her. I deduce this from 3 pieces of information; her family does not tolerate 'losers', the MC defeated a lot of people in Black Bouts (most probably to save his sister, Karen), and Mizuha's family is famous in Black Bouts. It could also be 'childhood friends' kind of event, before the MC got taken away to play in Black Bouts.