Houkago no Ghost

Scaredy-cat Shinji Takasaki gets forced to take a picture in the science room after school as part of a punishment game, where he comes across the self-proclaimed ghost Sagara. Sagara, who tells Shinji he's "interested" in him, says he'll curse him if he doesn't come back to visit the science room. The more time they spend together, the less Shinji feels like he was forced to be there... But ghosts like Sagara have to move on eventually, so how long can they keep this up?

(Source: Fantasista Inc.)