Rin Shiraki works as a courtesan in Kure's red-light district during World War II. Her childhood involved destitution, leading her to seek refuge on the rooftop of Suzu Urano's grandparents' home in Hiroshima. There, a young Suzu offered her watermelon—a kindness Rin remembers when they later reunite in Kure after Suzu marries and moves there. The two reconnect when Suzu becomes lost in the city. Rin initiates a friendship, frequently visiting Suzu and providing emotional support. During these visits, Rin perceptively questions Suzu about her feelings on motherhood and wartime pressures, helping Suzu confront her anxieties. Unbeknownst to Suzu initially, Rin once had a relationship with Suzu's husband, Shusaku Hojo, having been his client before his marriage. Suzu's discovery of this connection creates marital tension, deepening her insecurities and causing her to compare herself unfavorably to Rin's perceived grace and confidence.

Rin's circumstances as a sex worker make her vulnerable during the war. She subtly warns Suzu against visiting her district, hinting at the dangers and stigma of her profession. Later, when Suzu learns of bombings near Rin's brothel, she urges Shusaku to check on Rin's safety. Shusaku finds the brothel destroyed, confirming Rin's death in the attack. This loss illustrates wartime tragedies affecting ordinary lives. In the extended version of the adaptation, Rin's subplot receives fuller development. Her interactions with Suzu include discussions about Rin's difficult past and her observations about Suzu's relationship with Shusaku. These scenes emphasize Rin's role in highlighting Suzu's emotional growth and the complexities of human connection amidst hardship.