Takao Kasuga life is boring. Each day passes much like the one before, an endless cycle of going to school, coming home, sleeping, and then starting it all over again. Instead of doing the things that his friends do, Takao focuses his time on reading literature instead, in particular Charles Baudelaire’s Fleurs du mal. But something inside him is reaching its breaking point, and a flower of evil is about to bloom.

Takao steals Nanako’s gym cloths in a fit of stupidity and confusion, which weights heavily on his conscience as he sees the effect his actions have. Plagued by guilt, Takao is approached by Nakamura, who reveals that she saw him take the gym cloths. Takao’s problems continue to multiply as he’s slowly caught in a web of sin.

Forced by Nakamura into Saeki’s gym cloths, Kasuga finds himself blackmailed into spending even more time with his tormentor. Strangely though, when Nakamura is accused of stealing money Kasuga finds himself standing up for her.

Having stood up for Nakamura, Kasuga finds himself at odds with the rest of his class. But just when it’s looking like things can’t get much worse for him, his idol, Saeki herself tells Kasuga that she though it was very cool of him to stand up for the strange girl. Armed with a tiny fleck of light in the growing gloom of his life, Kasuga is elated and even finds it in himself to ask Saeki on a date, which she surprisingly accepts. Kasuga tries to keep it from Nakamura, but when she inevitably finds out about the impending date, Nakamura decides to push Kasuga even further into the darkness.

Saeki tells the whole class that she and Kasuga are going out. Kasuga gets nervous when he sees Nakamura talking with Saeki, wondering if she is revealing his secret.

Nakamura and Kasuga slowly walk home, hand in hand. The next day, the whole class is in uproar. The ink covered Kasuga's name. Saeki is devastated, her clothes at the center of the destruction. The whole school gets informed. Kasuga pukes. Saeki confronts Kasuga, having noticed that the drawing on the floor was the same as on his favorite book. He breaks up with her.

Saeki refuses to break up. The next day, Kasuga is absent. Saeki asks Nakamura what her relationship with Kasuga is. She says she's contracted to reveal his deviance. Saeki argues he's not a deviant. She goes to Kasuga's house and make a case for him through the window. His mom finds his stained clothes and he runs away. Saeki sees his mom looking for him.

One month later it is summer. The three have been ignoring each other. On Kinoshita's initiative, Saeki and Kasuga talk, only to break up. Kasuga is a shell of his former self. His mother is upset. He pukes. He knows Saeki is going to be alright without him, but even in his dreams, he can't stop thinking about Nakamura.

Kasuga writes an essay to Nakamura. Kinoshita asks Kasuga's friends what is wrong with him. Kasuga tries to give his essay to Nakamura, but she ignores him, so he starts reading it to her. She runs away. He goes to Nakamura's house to deliver the essay. On the doorstep, he is invited in by her father, who says that Kasuga is her first friend.

Kasuga enters Nakamura's room. He finds her diary and starts reading it. He recalls what had happened. Nakamura comes back, seizes the diary and runs away. He follows her and catches up to her. This time, he asks her to make a contract with him: they'll do what they can in order to leave for good someday.