Tsutomu helps his sister-in-law, Mai, manage the family flower shop while her husband, Shigeki, works far away. Overwhelmed by loneliness and the burdens of motherhood, Mai enters into a forbidden relationship with Tsutomu. As they welcome a new employee, Kozue, the two must navigate their guilt and keep their illicit affair a secret.
After noticing Kozue's loneliness and jealousy, Mai encourages Tsutomu to take her on a date to cheer her up. The outing leads to a romantic encounter that leaves Kozue conflicted about her growing feelings, prompting Mai to suggest a bold solution: sharing Tsutomu between them. The three eventually enter into a secret arrangement, embracing their mutual attraction in a daring new relationship.