The Kouda sisters watched their father leave them to start a life with his mistress 15 years ago. Soon after their mother abandoned them, forcing their maternal grandmother in Kamakura to raise them. Now a working adult, Yoshino Kouda receives a phone call with news from her older sister Sachi: their father has passed away from cancer. Although Yoshino is not distraught by the news, she—along with her younger sister Chika—feels obliged to go to the funeral, as Sachi is unable to due to her work schedule.

At the ceremony, the pair meet Suzu Asano—their 13-year-old half-sister. After Suzu's own mother's death, their father remarried. Suzu became the one to shoulder every responsibility, including taking care of her father's deteriorating health. Despite Suzu being a living reminder of their father's infidelity, Yoshino and Chika cannot help but feel sorry for her.

Surprisingly, Sachi arrives at the burial as well, witnessing the struggles Suzu has gone through. A newfound sympathy makes Sachi decide to bring Suzu into their immediate family. The four women must now learn how to navigate through life and come together as sisters.