Kiss Him, Not Me.

Kae is a fat high school girl who is a 'fujoshi', which is girls who enjoy reading homosexual romance novels. She is dismayed when her favourite character is killed off. She is unwell and refuses to eat. She loses weight. As a side-effect she is thin and suddenly popular at school. Boys begin to pursue her. She has a choice of suitors and can pick a boy of her liking. They are all pretty.