Treasure Ship: Latitudes of Lust.

Newly married Kazuo is troubled by the word "Takaraboin" that his wife Chiharu muttered in her sleep. One day, Kazuo learns from his uncle Kenji that "Takaraboin" is a sexual position. When Kazuo finds out that Chiharu had been dating Kenji before they were married, he decides to take revenge together with Kenji's wife.