Sutea Kōroya is a first-year middle school girl with hip-length light-brown hair tied in low pigtails secured by dark-green scrunchies. A single distinctive strand of hair often sticks up from the middle of her head. Her eyes are blue, and she typically wears a standard school uniform, sometimes favoring boyish styles despite a private fondness for cute things like maid outfits and shoujo manga.

Her body reacts abnormally to heat, diagnosed as thermophobia, causing discomfort or adverse reactions to warm temperatures or physical contact. This condition prevented her from outdoor activities as a child. Her childhood friend, Koshi Nagumo, adapted by cooling his hands before touching her, enabling her to play and forging their close bond. This history fuels her deep affection for Koshi, though she struggles to express it openly.

Sutea embodies a tsundere archetype, often displaying outwardly harsh or violent behavior—especially toward Koshi—that masks underlying care and vulnerability. She frequently uses the masculine pronoun "ore." When embarrassed or emotionally conflicted, she reacts physically, such as hitting Koshi, followed by immediate self-reproach and her characteristic catchphrase: "Why did I do that? I’m so dumb!" Her inability to acknowledge romantic feelings leads to vehement denials and jealousy, particularly regarding Koshi's interactions with the female residents of the Goddess' Dormitory. Upon learning he lives there after his house fire, she confronts him about his lack of communication and initially views the dorm residents with hostility and suspicion, seeing them as rivals.

Over time, Sutea reconciles with the dorm members. Observing their genuine kindness during a group trip prompts reflection on her own behavior, leading to apologies and improved relationships. Despite lingering jealousy, especially toward Atena Saotome, she begins cooperating with the group, signaling emotional growth. Her thermophobia remains a consistent challenge, requiring accommodations like ice packs during physical contact.

Her surname, Kōroya (香炉野), combines "incense burner" and "field." Her given name, Sutea, originates from the Basque word for "fire." The cultural term "orekko" (a girl using "ore") also describes her identity.