To Every You I’ve Loved Before

Takasaki Koyomi is a boy who lives with his mother after his parents divorce. He attempts to make friends in his new college prep school, but his social awkwardness combined with an atmosphere of focusing on studies means he is unsuccessful. One day, his classmate Takigawa Kazune approaches him, and tells him that she is actually from World Line 85, where she and Koyomi are lovers.

(Source: Anime News Network)