Omori

Since the terrible tragedy of four years ago, Sunny hasn't set foot outside his house. Now, in an attempt to shake him out of his torpor, his family has decided to leave Faraway Town. Three days before the move, Sunny's childhood friend Kel shows up to hang out one last time—but the world outside the young shut-in's door has changed completely, and Sunny's reunion with his old pals goes from bad to worse. Whether by chance or fate, the chain of events that begin to unfold calls up a past they all thought was buried forever...

(Source: Kodansha USA)