Tsutomu Katsuragi is a college student residing with his older brother and sister-in-law, Mai Katsuragi, after the death of their parents years ago. He helps Mai manage the family flower shop, a business founded by their parents. His brother's frequent and prolonged business trips leave Tsutomu and Mai alone together in the house.

This isolation exposes Mai's loneliness and unmet emotional needs. Tsutomu's own long-suppressed romantic feelings for Mai surface more openly during these times. He initiates a physical relationship with her, disregarding conventional moral boundaries due to their familial tie. Their interactions remain tense and complicated; Mai sometimes acts the next day as if nothing happened between them, prompting Tsutomu to actively pursue her further.

Kozue Takama, Mai's friend hired to assist at the flower shop, quickly perceives the unconventional dynamic developing between Tsutomu and Mai. Kozue's own loneliness, resulting from her husband's frequent absences, colors her perspective on their relationship. This situation weaves a complex emotional dynamic involving all three characters.

Physically, Tsutomu is an adult male with short brown hair reaching his ears and gray eyes. His background focuses on navigating familial obligations, personal desire, and the consequences of his choices within the confined setting of the household and flower shop.