Sayu is a third-year student at Higashi Elementary School (Class 4). Her family is well acquainted with Kei Amane's, and as a result, the two consider each other like sisters.

Whenever Kei's parents are away, Sayu often comes over to cook for her, as Kei struggles with cooking. She was the one who initially introduced Kei to Kiramon, but over time, her own interest in it faded.