Asao Atsuko works at the bento shop “Yonesuke” in Yanaka, Tokyo. Iwaki Kohei is a patent attorney who handles procedures related to patents and other intellectual property on behalf of his clients. The two met in university and, twelve years later, are still living together. They have a close, comfortable relationship—sharing meals every day and noticing even the smallest changes in one another, leading a life they are content with. However, Kohei ends up having a one-time affair with his colleague, fellow patent attorney Takano Yuko. Standing at a crossroads in their lives, the three struggle with hesitation, emotional drift, and stubborn pride. What kind of “family” will they ultimately arrive at?