Mayumi Mishima (Kanji: 三島まゆみ, Rōmaji: Mishima Mayumi) is a childhood friend and classmate of Ryo Hazuki from kindergarten to junior high school. She is also the oldest daughter of Fusayo Mishima and Takanobu Mishima and the older sister of Megumi Mishima.
Mayumi didn't notice her feelings for Ryo until she entered a highly competitive girls high school and was separated from him. Rather passive by nature, she feels nervous when in the company of both Ryo and Nozomi Harasaki, as she knows how Nozomi feels for Ryo. She tries to keep some distance from Ryo, as she would rather stay friends than confess her love to him. Anyway, she is occupied with entrance exams at the moment. She is dreaming of becoming a diplomat, but to do so, she must study hard to enter a university of foreign languages and learn Chinese. She sometimes walks around Dobuita and if she comes across Ryo, let alone if he speaks to her, she is happy for the rest of the day.
- Mayumi's zodiac sign is Sagittarius and she has a B blood type.