Kumiko is an ordinary housewife. Her husband Kunio is an ordinary office worker, who cares for his wife and enables her to lead a carefree life. But somehow Kumiko feels that something is missing in her life. She enrolls in a writing class at the community center and throws herself full-heartedly into her new task of becoming a good writer. In order to do so and encouraged by her teacher Oikawa who wants to lay her she decides that she must also explore the dark sides of life. She follows Oikawa to a love hotel to learn how adultery feels like.
Akiko, a fellow writing-class mate, is jealous about Oikawa starting an affair with Kumiko and neglecting herself. She tells Kunio about his wife’s affair, but to her surprise Kunio consents to his wife’s extramarital relation — which, Kumiko assures him, strictly serve the purpose of improving her abilities in writing. Determined to go all the way, Kumiko does not hesitate to also enter dangerous grounds.
Things get complicated when she is strangled and dies during one of her sexual explorations. As a ghost she learns some unexpected truths, but will she ever be able to tell her husband that she made the right decision?
Of the four so-called shitenno-directors Sato Toshiki was the only one who successfully tackled comedy, a sub-genre rather underrepresented in Kokuei’s line-up. In scriptwriter Kobayashi Masahiro, whose directorial works are far from being funny, he found a congenial partner, and together they created some of the wittiest comedies of the 1990s, not only in the pink film genre, but in Japanese cinema in general.
Adultery Diary starts off as a comedy in typical Sato Toshiki-style with strict shot-counter shot conversations recalling scenes from the late films of Ozu. But halfway trough the film shifts to a more somber tone without, however, loosing its humor and sarcasm. The film was chosen Best Film at the 1996 PG Pink Film Awards. In addition, lead actress Hazuki Hotaru won the Award for Best Actress and Kobayashi Masahiro the Award for Best Screenplay.