The Devil Does Exist(1998)

Akuma de Sourou

High school is hard for Kayano. When she tries to confess her love to the kind but distant Yuichi, the school bully Takeru makes her life hell. But things get worse when Kayano's mother gets engaged to Takeru's father, the school principal!

Soon enough, instead of be in love with Yuichi, she falls in her love with her future brother, Takeru.

What will she do about this forbidden love?

Included one-shots:
Volume 5: July
Volume 11: Flying Rabbit