Amane Suō is a third-year student at Mihama Academy who presents the image of a mature and nurturing older sister to those around her. Due to having skipped a school year at her previous institution, she is approximately two years older than the protagonist, Yūji Kazami. Physically, she is tall and has a well-developed figure, with long reddish hair that she often styles with ribbons. Her family runs a long-established restaurant in Tokyo's Ginza district, a background that has made her highly proficient in cooking.

On the surface, Amane is known for her cheerful, flirtatious, and often perverted sense of humor, frequently making suggestive jokes and attempting to seduce Yūji. However, this playful demeanor masks a deeply nurturing core. She naturally assumes a caregiving role among her peers, acting as a dependable big sister to most of the academy's students. This maternal instinct is strongest in her relationship with the much younger Makina Irisu, whom she treats almost like a daughter, earning her the nickname mom from the girl.

Beneath this outgoing and caring exterior lies a profound psychological trauma that serves as the primary driver of her actions. In her middle school years, Amane was one of the survivors of a catastrophic bus accident that left her and her basketball teammates stranded in a remote, forested crevice. As food ran out, the situation deteriorated into madness, and all but Amane and another girl, Kazuki Kazami, resorted to cannibalism. In a desperate escape attempt, Kazuki sacrificed herself to allow Amane to flee. Amane eventually found her way to safety, but she was the sole survivor. The media sensationalized the tragedy, with speculation that she had also engaged in cannibalism, which compounded her immense survivor's guilt.

This traumatic event defines her role in the story and her relationships. When Yūji Kazami transfers to Mihama Academy, Amane immediately recognizes him as the younger brother of Kazuki, the girl she believes died saving her life. Her intense interest in Yūji, which she initially frames as love at first sight, is rooted in a desperate need for atonement. She dedicates herself to helping him in any way she can, viewing her service and even her romantic advances as a form of penance for her perceived failure to protect his sister. This guilt also manifests in her big sister personality, as taking care of others becomes a way to compensate for the past.

Throughout the narrative, Amane's development involves confronting this survivor's guilt. Her cheerful and promiscuous front is a coping mechanism, and her personal arc forces her to revisit the horrors of the Angelic Howl incident, as the bus crash is known, to find a way to forgive herself and move forward. Her key relationships, particularly with Yūji and Makina, are instrumental in this process. Yūji represents both her sin and her chance for redemption, while Makina allows her to express the maternal care that was stolen from her in her own lost youth.

Beyond her interpersonal skills, Amane possesses several notable practical abilities. She is an exceptional cook, capable of preparing a wide variety of dishes thanks to her family's restaurant background. She also has a deep interest in automotive mechanics and has acquired a motorcycle license, owning a customized dirt bike named Boba Tarou that she keeps in the academy's garage. Her skills behind the wheel are extensive, and she has demonstrated the ability to operate not only motorcycles but also cars, minibuses, and even a seaplane.