Atsuko Asao and Kouhei Iwaki are a couple in their late twenties who have been together for nine years and living together for five. Both feel they have reached a comfortable but stagnant point in their relationship, recognizing that despite their age, they do not feel any more like adults than they did a decade ago. The story begins when Kouhei has a secret one-night stand with his coworker, Yuko Takano, an act that immediately complicates the stable, domestic life he shares with Atsuko. This betrayal forces both partners to confront nagging, long-avoided questions about their work, their future, and the prospect of starting a family.

The manga is set in the Yanaka neighborhood of Tokyo, a district known for its traditional shitamachi atmosphere. Atsuko works as a vendor at a bento box shop called Yonesuke, while Kouhei is employed as a patent attorney. The narrative follows the emotional fallout of Kouhei’s infidelity, exploring how the couple and Yuko navigate their new reality. The three characters find themselves at a crossroads, stubbornly and indecisively grappling with the very definition of what a family should be.

Notable narrative arcs include the initial revelation of Kouhei’s affair and the subsequent deterioration of the long-term relationship, the professional and personal pressures on Atsuko as she reevaluates her life, and Yuko’s own perspective as the other woman. The story also examines the wider circle of friends and family who influence the central couple’s decisions, including Atsuko’s college confidants and her father, as well as Kouhei’s mother. As the series progresses, the characters must ultimately decide whether their connection can survive this breach of trust or if they will choose entirely separate paths as they bid farewell to their adolescence. The manga ran for a total of 38 chapters, compiled into five volumes.