エンジェルノート

Taika Mugen, a high school boy, sees a girl with a face just like his own. When she touched a bird, the girl sprouted angel-like wings from her back and flew through the air. Taika's father, a molecular biologist, tells him that she is his sister Shinka, but also his clone. She must be restored to her original state by contacting her DNA. Taika succeeds in returning Shinka to her human form by kissing her on the mouth. Thus, the slapstick days of Taika and Shinka begin. (Source: Mangapedia, translated)