Mutsumi Sendou is a student at St. Mihailov Academy and a supporting character in The Qwaser of Stigmata. She is a seventeen-year-old girl with very long orange hair that falls past her hips and green eyes. In the series, she initially served as the first Maria, or living saint, for Alexander Nikolaevich Hell, known as Sasha, providing him with the vital energy known as Soma that Qwasers require to use their powers. After Sasha left the organization Athos, Mutsumi encountered Taisuku Fujiomi, nursing him back to health and eventually becoming his partner and lover. Her role in the story is primarily that of a devoted and fiercely loyal companion to Taisuku, acting as his Maria and a source of comedic relief.

Mutsumi is upbeat, cheerful, and very open about her feelings and desires. She rarely lets her inhibitions restrain her and is bisexual, often flirting with Mafuyu Oribe to the latter's dismay. Despite her carefree and occasionally mischievous personality, she is reliable and keeps Taisuku's wilder actions in check, sometimes using a paper fan for comedic punishment. Her motivations are rooted in her deep loyalty to her partner and her desire to support him through the conflicts they face. She also demonstrates a protective side, capable of defending herself with a pair of bladed tonfa in combat.

Her key relationships include her past partnership with Sasha, which ended when he left Athos, and her current romantic and spiritual bond with Taisuku Fujiomi. Among the other members of Athos, she maintains a friendly but straightforward demeanor. Mutsumi's development is not heavily emphasized in the narrative, but her transition from Sasha's partner to Taisuku's shows her adaptability and capacity for forming deep emotional connections. In combat, her primary ability is providing Soma to her Qwaser, but she is also physically capable enough to wield tonfa effectively, making her a practical asset in battle.