Kishibeno Yuri (Matsu Takako) meets her sister Tono Misaki's daughter Tono Ayumi (Hirose Suzu) at her sister's funeral. Ayumi cannot accept her mother's death, nor can she open the last letter her mother left behind. Yuri attends a class reunion to announce her sister's passing, and coincidentally, her first love Kagami Shiro (Fukuyama Masaharu) also comes. The two connect the stories of the three through letters.