Alisa Ayase is the younger sister of Eli Ayase. She initially attends middle school before enrolling as a first-year student at Otonokizaka High School, later becoming a third-year student by the end of the film's timeline. Due to spending a significant period living in Russia with her grandmother, she is initially unfamiliar with some Japanese customs, once mistaking a canned oden snack for a typical beverage. She has light blonde hair, blue-green eyes, and is often seen with a snowflake-shaped hairpin on the right side of her head.

In terms of personality, Alisa is characterized as gentle, shy, and understanding, presenting a more reserved and softer contrast to her older sister's more assertive nature. She is a devoted and enthusiastic fan of the school idol group μ's, demonstrating a deep admiration for its members and activities. This passion is evident in her emotional reactions, such as her visible excitement when meeting Umi Sonoda and her disappointment when she believes Umi does not recognize her. She is also forthright in her opinions, notably telling her sister Eli that she disliked a speech she had given, and questioning whether it truly reflected what Eli wanted to do. Alisa shares a verbal tic with her sister, the Russian exclamation "Khorosho!" (Хорошо!), which she pronounces with a more authentic rolled 'r' sound.

Alisa's primary motivation is her deep admiration for μ's. Her initial role in the story is as a catalyst regarding her sister's involvement with the group. When Umi Sonoda discovers her listening to an unreleased live performance recording, Alisa explains that her sister recorded it for her, indirectly revealing Eli's secret interest in μ's despite her public opposition. As the story progresses, Alisa becomes a committed supporter, attending μ's live performances and expressing her desire to one day join the group when she enters high school.

Her key relationships include her bond with her sister, Eli, for whom she cares deeply and is not afraid to challenge. She also forms a close friendship with Honoka Kosaka's younger sister, Yukiho Kosaka, who is her classmate and shares her interest in school idols. Among all the μ's members, Alisa holds a particular admiration for Umi Sonoda, being a dedicated fan of hers.

Alisa's character shows notable development, specifically concerning her dream to join μ's. After successfully enrolling in Otonokizaka High School, she eagerly looks forward to becoming a member of the group. However, as the third-year members of μ's, including her sister, approach graduation, Alisa comes to the realization that μ's is a unique and irreplaceable group comprised solely of its original nine members. She decides to give up her personal ambition to join them, believing that the μ's she loves does not include herself. She shares this decision with Honoka Kosaka, which helps solidify the remaining members' resolution to end μ's activities after the third years graduate. Instead of being discouraged, Alisa, together with her friend Yukiho, resolves to form a new idol unit and carry on the spirit of school idols at Otonokizaka. By the film's conclusion, both she and Yukiho are seen as third-year students and active members of the school's Idol Research Club, where they introduce the legacy of μ's to new students.

While not a performer, Alisa possesses notable abilities, including her knowledge and practice of μ's choreography, often practicing their dances at home and even teaching them to Yukiho. Her clear pronunciation of the Russian phrase "Khorosho" is highlighted as being more accurate than her sister's.