|Class and Year||1-F|
|Physical and Vital Statistics|
|Manga||Volume 1 Chapter 3|
Tsumugi Ryuukishibara is a schoolmate that is rumored to have been with the school before it was built that her peers call her "baba-sama" (elderly woman). She appears as a young girl with a bonnet. She acts like a grandmother towards Souta.
She has a strict and smart personality. She gave Souta and the others advice about cleaning and making a new dormitory.
She is called the elder of the school and it is said that she has been around since before the school was built. She is one of the seven mysteries of the school. She is also the living dictionary of the school.
- Her exact age is unknown but she has made several comments that lead onto reveal she is at least sixty.