OUSAMA TO FUSHIGI NO SHIRO

From Chibi Manga:

Our main character, Mitsu, fall in love at the first sight with the brilliant son of a noble familly, Hiroto. Thank to some miracle, Mitsu start to go out with him but then she discover that this guy is a sadistic prince...


from Sound of Jewels:

She entered in that expensive school because she wanted to meet the prince of this school.

But then she became his target and it looks like this boy is in fact really sadistic! What will she do...?