Nagasawa Takashi is your everyday normal high school guy, he's a geek and has a crush on a girl. A member of the biology club, one day he gets bitten by a mouse and freaks out thinking that he is going to get the plague. One night whilst walking home from school he comes across an accident scene where he gets attacked by a large rodent-like creature and is bitten. He is tended to by a mysterious doctor, and soon notices changes in his body—owing to the contraction of the disease "Nightshift."