Yui and Takashi have been close friends since college, and Takashi is now happily married to his wife Miki. Yui, the same age as the couple, remains single and works as a successful career woman in the publishing industry. She occasionally visits their home after work to drink and chat, sharing a warm, comfortable friendship with both of them. One night, when Takashi learns his wife Miki is away overnight, Yui stops by his place. Alone together, an unexpected tension arises between them, shifting the dynamic of their relationship forever.