Insomniacs After School

Two sleepless teenagers find kinship as they escape to their school's astronomy observatory. Unable to sleep at night, Ganta Nakami is cranky in class and unpopular with his classmates. He discovers that the school observatory, once used by the now-defunct astronomy club, may be the perfect place for a nap—but he's not alone. Fellow insomniac Isaki Magari is willing to share the observatory with Nakami, and a friendship between the two begins as they bond over the most unlikely of things. <em class=de-emphasized>(from manga)</em>

Synopsis from Anime News Network