I have read a manga similar to Kenshin No Keishousha around 2013-2014, but I can't remember the title, all I remember is this guy who sees girls naked.
They talk with the principal and the girl challenges the guy to a sword fight. The winner becomes master or something like that. The school is a place where people summon swords magically or something like that. The girl summons her sword and the guy defeats her fast with his katana.
Then the girl asks the principal who the guy is. The principal says he is someone who was disowned by his family and has been repeating school for 2 years (not sure but I think it was 2), since his family is powerful and had influence at the school. The principal pitied him and removed the things hindering the guy from graduating (she was not the principal 2 years ago).
The principal also says the guy was able to beat her. The girl and the guy become friends and girl tries to make moves on the guy.
The guy and the girl live in same room.
Everything I have said above is from chapter 1 to 3 or maybe 4/5 but not more than that.
The guy had a little sister if I remember correctly, and the girl is like a princess. I think it was harem.