Mutsuki Uehara, affectionately nicknamed "Mucchii," is an athletic student renowned for her tomboyish demeanor and exceptional physical prowess. Her reputation as a skilled athlete attracts invitations from multiple sports clubs seeking her as an honorary member, though she initially holds no official position in the student council. Driven by a natural inclination to help others, she actively contributes to council projects, eventually earning the role of assistant through her dedication.

Contrasting traditional femininity, she sports a short haircut, speaks with a deeper voice, and exhibits informal mannerisms—like enthusiastically patting classmates on the back during conversations. Her longstanding friendship with Mei Etoh, dating back to elementary school, sees her persistently encouraging Mei to connect with peers. Early in high school, she bonds with Mika Inamori, maintaining their friendship despite contrasting personalities.

Within the student council, she aids in initiatives ranging from remodeling the council room to organizing inter-school events like dodgeball tournaments. Her collaborative spirit and focus on boosting school morale cement her integral role in the council. Central to her history is her talent for bridging gaps between reserved classmates, fostering unity through efforts like integrating Mei into group activities.