Okay, so some mentally unstable and sexually repressed man saw an underage girl on a train and "fell in love" with her, he followed her when she got off the train, raped and killed her, probably beheading and burying her at the train station. He's obviously crazy and suffering from delusions. He's hiding out in the no name town where he killed her. Apparently the girl he killed had a reputation for being "loose", so no one's really searching for her that hard. He wants to return to Tokyo and pretend it never happened, but the fear of her body being discovered traps him there, the changing time and seasons pulling him deeper into hell.
Or at least that's my interpretation of it. Could also just be a metaphor for sex addiction