Chiaki Honda, a middle-school boy with bright green hair, chooses to neglect his studies in favor of smoking. One night, he accepts a dare from Nanako Kikuchi at the arcade, with Nanako wagering her body against Chiaki's watch. She emerges victorious, leaving Chiaki fuming. Nonetheless, Chiaki's lifestyle remains unchanged. While riding the train the next day, Chiaki stumbles upon an odd young man who bears a striking resemblance to him. Eventually, Chiaki and Nanako cross paths again.