Mito and Yamagishi live in the same neighborhood. Once a month, they will host a home party together, where they drink and talk about life. However, a few days later, Aika has a fight with her husband and she wants to go back to her mother's house. Kana constantly advises her to stay at her place to reconsider. At the same time, Aika's husband becomes very ill, and Kana stays at Aika's house to take care of him. Kana's kindness touches Aika's husband, and due to not having sex for a long time, he cannot control himself and has sex with her. Kana's husband witnesses this through the window and decides to have sex with Aika to get revenge. Not stopping there, he forces his wife to have sex with him in front of him, so that he can also have sex with Aika in front of her husband to seek revenge. However, it seems that they are gradually getting immersed in the excitement of having sex together, so their relationship becomes closer and in the future, they will have sex together every month to strengthen everyone's relationship...