Sumire Ryuzaki  

Coach, 竜崎 スミレ

Sumire Ryuzaki is both the tennis club's coach at Seigakus school and a math teacher there. She played an essential role in developing Nanjiro Echizen's skills, making her one of his mentors. Additionally, she is Sakuno's grandmother. Her former mentor, Mikiya Banda, also known as Banji, coaches Yamabuki. Despite their rivalry, Sumire is highly regarded for being a reliable and great coach. She has a close relationship with her regulars and participates in recreational activities such as bowling reunions and beach-volley mini-tournaments with Rokkaku Middle School.