Aine is a high school student and the female protagonist of the story. She is a shy and somewhat introverted girl who aspires to become a professional songwriter, spending much of her free time writing lyrics. Her life takes a dramatic turn after a chance encounter with Sakuya, the lead singer of the popular rock band Lucifer, who discovers her work. To protect her identity from obsessive fans and the music industry, she writes for the band under the male pseudonym Yukihiko.

In terms of personality, Aine is depicted as sensitive, kind, and initially very naive. She often displays a lack of confidence and struggles with low self-esteem, largely due to her ordinary background compared to Sakuya’s fame and the world of celebrity that surrounds him. She tends to be trusting, sometimes to a fault, and can be easily flustered or jealous, particularly when faced with other women pursuing Sakuya. Despite these insecurities, she has a resilient core that begins to surface as she endures various trials.

Her primary motivation is her desire to write music and prove herself as a lyricist, a role that becomes increasingly intertwined with her personal life. She is driven by her love for Sakuya and her wish to support the band’s success, even as she struggles to reconcile her professional ambitions with the intense emotional and physical demands of her relationship.

Within the story, Aine’s role is central as both the creative force behind the band’s sensual lyrics and the primary romantic interest of the lead singer. The band’s manager and Sakuya himself often push her to explore her own emotions and desires in order to produce the erotic content expected of Lucifer, making her personal experiences the raw material for their hit songs. This dynamic places her at the heart of the band's internal and external conflicts.

Her most significant relationship is with Sakuya, which is passionate, tumultuous, and marked by intense jealousy and protectiveness on both sides. She relies heavily on him for emotional support and protection, though his possessive nature and the obstacles created by his fame often put a strain on her. Other key relationships include her interactions with the other members of Lucifer, who serve as background support, and her parents, who are largely absent and inattentive, leaving her to navigate her life mostly on her own. She also forms a connection with the band’s producer, Hitoshi Takayama, who cares for her during a period of profound crisis.

Aine undergoes significant development throughout the narrative. She begins as an insecure and somewhat helpless girl who frequently doubts Sakuya’s love and her own worth. After suffering traumatic events, including a violent assault by a rival record executive, she falls into a deep depression and nearly takes her own life. This experience, combined with the subsequent death of a friend, serves as a turning point. She emerges from her trauma stronger and more mature, eventually finding the resolve to move forward and study to become a music producer, capable of standing on her own.

Aine’s notable ability is her talent for writing lyrics, specifically her knack for crafting sensual, evocative poetry that captures the desires of the band’s fanbase. Her creative process is directly linked to her emotional and physical experiences, making her vulnerability and passion a key part of her artistic identity.