Tatsuo Kouzuki, a son who lives alone while attending university in Tokyo. For the purpose of home renovation, brothers Yōhei Fujishita and Yasuhiro Fujishita, along with their aunt Rika Fujishita, are staying at the house of Tatsuo's mother, Akari Kouzuki. In other words, they are living at Tatsuo's family home. One day, Tatsuo brought his girlfriend home as planned for a visit, but he couldn't suppress his sexual excitement towards his mother and ended up having sex with her multiple times, leaving his girlfriend aside in his obscene fantasies. At the same time, Yasuhiro witnessed his own mother Rika and Yōhei having sex, envying their relationship so much that it made him jealous. Moreover, he also witnessed the incestuous act between Akari Kouzuki and her son.
