Tokyo, September, 1971. The bodies of a wealthy couple, Rintaro Oki and his wife Junko, are found in their house. At first, police suspect that Oki's nephew Takahiro is the criminal, but a friend of his, Akihito Sugiura, gives him an alibi. After that it's concluded that Oki's driver Shuuji Tazawa is the criminal. Tazawa commits suicide one week later and the case is closed.

33 years later, December 2004. Hoshi Sugiura is engaged to the receptionist of the company, Keiko. Later a happy Hoshi comes from the party to home and discovers his father Akihito's hanging corpse. The police conclude that he committed suicide. Hoshi recalls his father having said the morning of that day something about reading an old diary. The content of the diary tells the story of how he gave an alibi to Takahiro concerning a crime in the house of a married couple 33 years ago. When Hoshi question a friend of his father, who came to make a visit of condolence, closely about that incident, he advised him to forget it if he wants to be happy. Later he receive a phone call from his fiance shouting "Help!" He goes quickly to her house and finds her near dead after being assaulted.

Hoshi thinks the cause of his father's death is related to that past crime and begins to examine that time's newspapers in the library. He obtains proof that his father's death is a murder and is determined to expose the crime. He receives a threatening call and later is abducted, receiving a brutal assault from yakuza henchmen, with his male function being lost.

One year later, November 2005. Henchmen of the Kuroishi yakuza clan gets killed by a beautiful woman, and a butterfly specimen is left near the bodies.

Hoshi is now living in the house of Keiko, a transvestite that helped him after the assault, and lives as a woman by the name of Kaoru. The revenge of Hoshi is just starting.