Kami-sama no Iutoori

Ayumi, a cheerful teen who's admittedly a bit stupid, is in love with her classmate Musashi. Before she can tell him how she feels, however, she sees a strange boy that no one else can see. He tells her that he's a god of death, and she only has one month to live -- so she'd better make the most of it and take her love once and for all!