Sae Nagumo attends Seikyo School and harbors romantic feelings for her classmate, Jun Igarashi. Her mother, Keiko Nagumo, is their teacher. Noticing Jun's frequent mention in household conversations, Sae confronts him directly to understand her mother's repeated references. This situation fuels tension as Sae's affection for Jun clashes with Jun's own attraction towards Keiko. Her interactions focus on navigating this complex dynamic between herself, Jun, and her mother.

Physically, Sae has dark ochre hair and brown eyes. She is 1.63 meters tall with body measurements of 85-57-86 and blood type AB.