I'm not sure if I'm recalling it right, but—didn't she throw Mei's clothes with the garbage (clothes that were likely her best clothes, probably even newly bought since it was her first college day and she wanted to impress) on the pretext that she didn't like their smell?
Oh gawd that scene!
If I wake in the morning and find that someone did that to me, I think I'd tell her:
"Oh baby, you're my milkplus! You get me in the MOOD FOR ULTRAVIOLENCE!"
Then I'd go Alex DeLarge on her ass. Grr.
I'm not getting any harem vibes? Oiwa is clearly interested in the third legendary ghost, not Ryouyo. Even if Okiku had any competition, the fact that her name is in the title kind of gives away the game.