Aya Komichi is a Japanese high school student with long dark blue hair, typically styled in high twintails, and dark blue eyes. She stands 159 cm tall with blood type A. Her standard school uniform consists of a navy blue sweater over a white collared shirt, a pink striped bow tie, a skirt, and black tights; this transitions to a black sweater vest and black thigh-high socks during summer. Her casual attire frequently features feminine dresses with ribbons, and she may wear her hair down without accessories.

Born on September 15, Aya attended middle school where she first met Yōko Inokuma. Initially highly dependent on Yōko due to her timid and socially withdrawn nature, Aya relied on her for support and guidance. Though this dependence lessened over time, she remains emotionally attached. During high school, she forms friendships with Shinobu Ōmiya, Alice Cartelet, and Karen Kujō. Academically capable, Aya passed entrance exams for a prestigious high school but declined the offer to remain with her friends. Despite her intelligence, she is prone to forgetfulness and occasional clumsiness, misplacing items like her lunchbox or accidentally damaging Yōko's notebook. Her personality blends level-headedness with extreme timidity; she embarrasses easily, particularly in situations involving Yōko, toward whom she harbors romantic feelings.

Aya struggles to express her emotions openly, often reacting to Yōko's proximity or physical contact with flustered denial, blushing, or panicked withdrawal. She envisions romantic scenarios with Yōko but typically responds with tsundere behavior—issuing insults, light physical hits, or coldness to mask embarrassment—after snapping out of these daydreams. Examples include refusing to swim for fear of needing CPR from Yōko, sharing food while envisioning couple-like feeding, or becoming jealous over perceived rivals. Her reactions are noticeable to peers like Karen and Shinobu, who tease or support her, though Yōko remains largely unaware. Aya's self-consciousness extends to body image, as she gains weight easily and experiences angst about her physique compared to others.

Her character development shows increased emotional resilience while maintaining core traits. In her second year, she and Yōko are placed in separate classrooms, causing initial distress, though she adapts while continuing to value their friendship. She assists Yōko academically, helping her complete assignments to avoid repeating previous failures. Aya also bonds with Honoka Matsubara, relating to her struggles in expressing feelings and offering support. By the manga's conclusion, she enrolls in the same college as Yōko and Karen, indicating sustained closeness. Throughout all media—including the "Pretty Days" OVA exploring her middle school past and the "Thank You!!" film depicting graduation—Aya's journey reflects incremental growth in confidence while retaining her earnest, if awkward, devotion to those she cares about.