Setsuna serves in the Simeon Girl Squadron under Simeon's upper management. She stands 165 cm tall with measurements of 89 cm (bust), 59 cm (waist), and 86 cm (hips). Her striped underwear becomes a distinctive trait recognized by characters like Cruz Schild.

She is highly devoted to her missions and openly states her strong loyalty and liking for Adam Arclight. As the self-appointed leader and oldest squadron member, she displays arrogance regarding her abilities, relying heavily on her power and teamwork in combat. Despite this pride, she fears higher-ranking individuals like the Shintenou, Saten. Setsuna remains level-headed during operations but tends to underestimate opponents; she initially gained an upper hand against Eve Neuschwanstein only to be defeated after Eve dismissed her punches as weak.

Her primary ability is the Speed fragment, enabling movement up to Mach 9. However, her ordinary kinetic vision limits its effectiveness to straight-line trajectories, impacting her combat in complex engagements, as explained during the St. Rose Academy Arc.

Setsuna interacts repeatedly with Cruz Schild. During their second encounter, she torments him; the manga depicts her stealing his locket and denouncing his weakness, leading Adam Blade to retrieve it and inflict heavy retaliation. Later, at St. Rose Academy—where she and Kuchinashi undergo retraining as punishment for their defeat by Blade—her attitude shifts after Cruz falls into the grounds. Recognizing Mio's panties among his belongings and due to his alliance with her squadron member, she hides him. She develops respect for Cruz's intelligence after his actions in Simeon Tower and tasks him with investigating bomb threats at the school. After failing to defeat Rin, she receives further retraining punishment.

Subsequently, she indirectly assists Cruz by physically compelling Rin to support his defense of a town against Hatfield, demonstrating her continued influence and operational role beyond direct combat.