Kagayaku Kisetsu E

Kohei Orihara is a Japanese high school student who has experienced much tragedy in his life. When he was a child, both his parents died. After he lost his little sister, Kohei became increasingly reclusive, and eventually creates an alternate reality for himself, called "Eternal World". This world resembles afterlife, though it is possible to return from it to the real world under certain circumstances. As Kohei forms relationships with the game's female characters, they begin to forget him after a while, which causes him to retreat deeper into the Eternal World. Only by creating a strong bond with one of these girls can Kohei return to real life.