Mata ne, Kamisama

Ryou is in love with class beauty Koutarou. As they get to know each other better, Ryou hears a strange rumor about Koutarou's family. One day, Ryou visits Koutarou's house and sees him giving up his body in the name of a ritual. As he hears his friend's reason to continue performing the ritual, Ryou makes a decision...

(Source: Hakusensha, translated)