Mayumi is the daughter of Saegusa Kouichi, the head of the Saegusa Family from his second wife, after the first died. Their family bears the number Seven (七) in their name and is one of the two most influential families among the Ten Master Clans. She has two older half-brothers and two younger twin-sisters, Izumi and Kasumi, making her the oldest daughter of the main family and the third child. Due to her position as the oldest daughter in the Saegusa family, her beauty and her exceptional ability is considered to be one of the "veritable rising stars among blue bloods."
Mayumi is a young lady who is known for her natural beauty. It is stated during her internal monologue that she stopped growing (height) in her third year of middle school, which makes her slightly shorter than average. Her limbs are described as quite long despite her short stature, and her chest is also large in proportion to her height.
She is the former Student Council President at First High School and the daughter of the 10 Master Clan's Saegusa Family.
Considered to be a prodigy in the magic community, she is nicknamed the "Elven Sniper" for her extraordinary talents in long-ranged precision shooting. She is also known as the "Elven Princess" for her beauty in tandem with her and innate magical ability. She was one of the "Triumvirate", the three strongest third year students at First High School, which also includes other notable students such as Katsuto Juumonji and Mari Watanabe.
Excluding her height, Mayumi is described as someone with a well-rounded personality and a feminine side. While it is hard to notice, she cares about others in her own unique way, so she fits the bill of being an "older sister" perfectly. She is generally quite confident in her appearance when in the presence of others.
(Source: Dengeki Wiki)
