Tokisaka-san wa Boku to Chikyuu ni Kibishisugiru.

Utsugi Sou, a high schooler that is very serious about taking out garbage on a daily basis. He lives alone and has a close girl friend. Lately, his garbage has been messed with and redivided by a stranger unknown. And, one day, a transfer student, Tokisaka Koyomi arrives and seems to know him; however, he has no clue. Later, he finds out that the transfer student is from the future. The story begins from here...