Nodoka, a high school girl who lost her mother to "gem disease," a mysterious illness that transforms the entire body into diamond, could not shed tears to mourn her mother. She has grown estranged from her younger brother Eto, her only remaining family, and struggles to fit in at school. One day, her beautiful classmate Mari asks her to become friends — but Mari, too, is afflicted with gem disease. A coming-of-age human drama written in an epistolary style using dialect, exploring questions of life, money, and the nature of beauty.

A story of a girl who lost her mother to gem disease, finding the courage to face grief through her encounter with a beautiful classmate who shares the same illness.