Fuuka hits a growth spurt in her second year of middle school and suddenly becomes very tall and curvy. Because her unusual hairstyle leaves only one eye showing, her classmates nickname her Saipuu, after the cyclops. Years ago, as a much smaller girl, she promised to marry her older brother Hikaru, and he played along with the sweet crush. Now she considers herself grown up enough to keep that promise, which unsettles him. With her model-like figure, her devotion becomes embarrassing and sparks misunderstandings at home and at school in this ecchi slice-of-life comedy.