Sharekoube, Tokuko

紗礼頭徳子

As one of the legendary Four Lords of Pastimers, she is a student at a prestigious nearby all-girls academy and was introduced by one of Chisato's friends, who is a teacher at that school. She stopped by during Episode 4 to socialize with the Pastimers Club.
Her name is revealed in chapter 73, along with the fact that she possesses multiple talents, such as performing rakugo and playing the koto.