Kisu Meguru Sekai

Synopsis

A 14 year old girl has a crush on her teacher, but can't muster the courage to tell him. When she accidentally kisses him she is transferred to a parallel world where he is a scientist. She finds out that he's an alien observer, and whenever she kisses him she goes to another world where he is a bit different. But in each world she finds that she still likes him. He gives her a device so that a version of him will be able to find her and save her on each world she goes to, until she finds a way to go back to her original world. Source: MU