2190-nichime no Yoru ni

Hikaru, a third-year high school student, is forced to stay with his cousin Manabu for family reasons. Hikaru is looking forward to meeting Manabu, whom he adored as a child, but to his surprise, Manabu has become an erotic manga artist!　 A boy's love story about a pure high school student and an adult manga artist living together. Source: Hakusensha, translated.