Spirit Of First Love(2003)

Hatsukoi no Shiryou

Tomo, who's tired of the unfaithfulness of his step-mother, makes friends with Yuuichi, who lives next door to him. An incident happened over the summer and Tomo believes that he will never fall in love with anyone and that it's meaningless. Yuuichi comforted Tomo by telling him that he will definitely fall in love with someone one day. And ten years later, Tomo didn't expect to serve as the spirit of a first love...

The cause of all misfortune is the curse of the first love.

(Source: Digital Manga Guild)