Laughing Target

When Azusia and Yuzura were mere children, they were betrothed to each other by their parents. Many years later, after Azusia's mother mysteriously dies, Azusia returns to Yuzura with the intent of marrying him. Of course, Yuzura has a girlfriend, Satomi, and this doesn't sit to well with Azusia. Add to the fact that Azusia is anything but "normal", and she has no problem eliminating the competition by any means possible.

Synopsis from Anime News Network