Thirty-five-year-old novelist Makio Koudai never had a good relationship with her older sister Minori, who always berated her for being different. Due to this, Makio is not stricken with grief upon hearing the news that Minori and her husband die in a car crash. But when Makio is asked to identify their bodies, she runs into her 15-year-old niece, Asa Takumi, whom she has not seen in years.

As Asa struggles to process her parents' death, Makio reassures her that her complicated feelings are valid and suggests that the teenager start writing in a diary as a way to cope with the loss. Upon learning that no other relatives wanted to take in Asa, Makio decides to become her guardian despite her lack of experience. In a world full of uncertainty, the novelist and teenager must learn to live with each other while figuring themselves out.