Tsukuyo Aoba occupies the position of the second eldest daughter in the Aoba family, situated between her older sister Yuzuki and younger sister Kurage. Her parents, both priests, became estranged; her father's whereabouts are unknown, and her mother relocated to serve as head priestess of Ryukoku-Ji Temple. Consequently, Tsukuyo and her sisters reside at Mikazuki-Dera Temple under the temporary guardianship of the custodian nun Kiki. The temple suffers financial instability and significant debt tied to Harukaze Akagami, placing the sisters at risk of eviction after high school graduation if its status remains unresolved.

Physically, Tsukuyo possesses blonde hair, typically worn in a short ponytail with two front bangs, and amber eyes. She stands notably taller than her sisters, maintaining a slim yet curvy figure, with her prominent bust size frequently emphasized and estimated as a G-cup. Her attire alternates between a standard high school uniform—a skirt, white shirt, tie, and sweatshirt—during school hours, and casual outfits like short jeans, skirts, sweaters, hoodies, knee-high socks, and loose jackets elsewhere.

Initially headstrong and defensive, Tsukuyo exhibited significant hostility towards Akemitsu Akagami upon meeting him. This stemmed from an accidental encounter where he saw her naked, compounded by his association with the Akagami family responsible for the temple's debt. Her hostility manifested in physical attempts to expel him and collaborative schemes with Mia Christoph. She harbored a deep, near-delusional admiration for Yuzuki, particularly regarding nonexistent archery prowess. A pivotal shift occurred when Akemitsu protected her from falling boxes, resulting in an accidental kiss. Following this, Tsukuyo displayed increasing vulnerability, evolving into a bashful and easily flustered individual around Akemitsu, especially in response to perverted behavior or romantic situations. Despite stubbornness, she demonstrated remorse, self-reflection, acknowledged her growing affection, voluntarily kissed him, and accepted her role as a love rival to Yuzuki.

Her relationship with Akemitsu transformed from intense animosity to genuine romantic affection. Key incidents shaping this included forced cohabitation at the temple, the bath-related nudity encounter, the life-saving box incident leading to their first accidental kiss (where she demanded a "kiss fee"), and his delivery of her forgotten lunch to school. These encounters revealed his kindness, altering her perception. She later intentionally forgot her lunch to facilitate his visits, sought his help reconciling with archery, and openly competed for his affection. Tsukuyo maintained a strong, protective bond with her sisters, idolizing Yuzuki despite later recognizing her lack of archery talent, and continuing to value their sisterly connection. She displayed affection towards Kurage but consistently reprimanded her for inappropriate sexual humor.

Character development is evident as Tsukuyo returned to archery after Akemitsu exposed Yuzuki's lack of skill and encouraged her rediscovery of the activity. She actively created opportunities for interaction with Akemitsu, like deliberately forgetting her lunch. Her willingness to defend him against misconceptions, imploring friends to understand him before judgment and collaborating on Valentine's chocolates, marked a departure from her initial hostility. Accepting her feelings culminated in her initiating a kiss with Akemitsu and consciously entering a rivalry with Yuzuki for his affection.