Majo Rumika no Akai Ito

A class rep Haneda Kotoya was tackled suddenly from the back, and trampled really hard. "Wha..!? What the hell?", just as he thought that a girl smiles unfittingly and says "Finally I found a man who really loves me." Since then the girl, Kirima Rumika, would come and trample him no matter what. Not just that, while she says, "this all is for Kotoya", she lockes and ties Mizukoshi on a chair in classroom for a night, because the girl often skips the class rep's job (she and Kotoya are the 2 class rep). And what exactly does Rumika want to do...? Source: JCafe