Mayumi's family owns a bathhouse and she often has to help out around her house. Although she usually, tries to find a way around it, much to her parents dismay. In addition to her bubbly and hyper personality, she is not very good at test-taking and often has low grades.
She has the smallest bust size in the series, a fact often made fun of by Rin and Itsuki. Nonetheless, she takes pride in her small breasts, rationalizing that by being below average they are a rarity sought after by a select group of men. It is revealed in Shuffle! Essence+ that she and Itsuki are childhood friends. It is hinted that she may show feelings for Itsuki, despite of their frequent quarreling. She becomes a winable heroine in Shuffle! Essence+.