Ahiru no Oujisama

Reiichi is in love with Yumiko, the prettiest girl at school, but believes his ugly appearance makes them an impossible match. After rescuing a magical dog from certain death, he receives one wish and asks to become beautiful. With his new appearance, Reiichi can approach Yumiko as the person he wants to be. But whenever he touches her while thinking lustful thoughts, he turns back into his old, ugly self.