Nagisa Himura attends Marehoshi Private Girls' Academy and performs as part of the idol unit TROIS ANGES with Amaha Shiratori and Kanade Hokaze. She embodies the unit's knight role, fiercely protecting Amaha and Kanade in all circumstances through unwavering loyalty and guardianship. Her appearance implies combat readiness, though her proficiency remains undefined.

She possesses long, pale brown hair secured in a ponytail by a thin blue ribbon. Her bangs sweep to one side, pinned by pink and yellow clips beneath tented layered hair, and feature two cowlicks—one upright. Sharp sapphire eyes accentuate her gaze. Casual outfits reflect a mature, nearly masculine style. During TROIS ANGES performances, she wears a white top with sky blue lining, gold straps, and ruffled off-the-shoulder layers in white, orange, yellow, and sky blue. Gold bead chains and a wing-like ribbon adorn the back. The ensemble includes sky blue and gold shorts with frilled trim, white boots detailed with sky blue lines and gold straps, a beaded necklace holding a droplet gem, and a scalloped gold-lined collar.

Nagisa reveres Amaha and Kanade as elder sisters, displaying protective instincts that occasionally cause her to misjudge situations. In turn, they cherish her as a younger sister. She enjoys safeguarding her unitmates and eating donuts, but dislikes horror films.