After three years of marriage that began as an office romance, Ririko now lives in Tokyo with her husband and his younger sister, Yu, who moved to the city to pursue her dream of becoming a photographer. Yu is slightly younger than Ririko, and Ririko has always doted on her like a real sister. One day, the husband leaves for a three‑day business trip, leaving the two women alone under the same roof. In principle, living together as two women should be easy and comfortable… but Yu carries a secret she has never shared with anyone. From the very first day she met Ririko, she has harbored feelings for her.