Tomoe Hiiragi stands 180 cm tall with a slim physique, pale skin, and measurements of 89-62-88 cm. Her striking violet hair features spiky bangs, twin tails, and a single antenna-like strand, complementing amber eyes with a distinct tsurime shape. As the fourth eldest and third youngest of six Hiiragi sisters, she presents a stern appearance that belies her fundamentally gentle, docile, and kind nature. Shy and timid, she avoids conflict, displaying pacifist tendencies and often enduring teasing from her sisters due to her low self-esteem. Her hobbies include meticulous gardening in the residence's backyard and cooking, frequently while wearing an apron.

A significant secret defines Tomoe: she transforms into a superheroine to combat the recurring enemy "The Claw," engaging in fighting that starkly contrasts her non-confrontational personality. Her room reveals a softer side, filled with numerous stuffed toys. All six siblings, including Tomoe, are adopted into the Hiiragi family. She navigates complex dynamics, acting as a younger sister to her elders and an older sister to the younger ones, including her interactions with the youngest adopted brother, Kuya Hiiragi, which blend care with gentle teasing from others.