Ayano Kasai attends high school alongside Ritsuka Uenoyama and Mafuyu Sato, sharing a classroom with Ritsuka and her friend Waka Kurihara. Her Persian orange hair and matching eyes are distinctive, complemented by her school uniform: a light brown cardigan over a white buttoned shirt with a red bow tied at the collar. Her hair gradually lengthens over time, becoming a recognizable feature. Standing 162 cm tall with an October 9 birthday and blood type A, she pursues the science course and aims for a Tokyo science university. Initially, Ayano exhibits jealousy and pettiness toward Ritsuka’s sudden closeness with Mafuyu, speculating about their relationship. This jealousy drives her to reveal rumors about Mafuyu’s past to Ritsuka, disclosing Mafuyu’s middle-school relationship with Yuki and Yuki’s death. Overwhelmed by guilt, Ayano tearfully apologizes, fearing permanent estrangement from Ritsuka. Afterward, Ayano demonstrates remorse, reflecting on her actions and shifting to support both Ritsuka and Mafuyu. She encourages Ritsuka to visit an ill Mafuyu, develops mutual understanding with Mafuyu, and offers him future advice, forming an unexpected friendship. Waka Kurihara observes their rapport, and both frequently attend concerts of the band "given" together. Ayano remains observant, noting the evolving dynamic between Ritsuka and Mafuyu. Characterized as thoughtful, sensitive, and reliable, Ayano prioritizes others’ feelings and engages in self-criticism when perceiving mistakes. Her logical, practical approach aligns with her science focus. Her name, written with "fire" or "flame" characters, reflects a background detail. As one of few female characters in a male-centric narrative, she possesses a "peculiar charm" according to the creator.