A female magical cat who works as a substitute principal until either one of the two missing principals returns. Uses a sentient magic book to cast her spells, the book being her close friend. The book is unable to speak, but Yuumi can understand it through intuition. Yuumi has an insane amount of mana, due to which is considered one of the strongest members of the academy, but she is proficient only in supportive spells. Appears to be strict on work, but is very childish in daily life.