Kisaragi Akiba is a central figure in the story, originally a celebrated music superstar in her youth before transitioning into a role as a singing coach and the head of a prestigious music school. Her past as an idol singer gives her an expert, intuitive understanding of the music industry and the qualities required to achieve stardom. Her personal history is marked by profound tragedy; she was tragically separated from her three infant daughters and later experienced the death of her husband, a starving artist named Yoh. Overwhelmed by grief and left to raise her young children alone, she fell into a deep depression and attempted to end her own life, an act she believed also claimed the lives of her daughters. This traumatic event left her with deep-seated survivor's guilt.

Following this period of loss, Kisaragi adopted a young girl named Reika, who had suffered abuse from her own mother. For Kisaragi, raising Reika and teaching her to sing provided a reason to live again, while Reika found the maternal care she desperately needed. Under Kisaragi's mentorship, Reika rose to become a major singing sensation, much like her adoptive mother before her.

Kisaragi's personality is complex, often coming across as strict, businesslike, and darkly seductive in her professional demeanor. She is a precise and intelligent manager who runs her school by mixing maternal instincts with a sharp awareness of what makes good pop music. Her motivation for creating the music school and a special Class S for elite students is rooted in her belief that Reika has learned all she can from her, and a desire to find and cultivate the next generation of musical talent. In her role, she acts as the overseer of the S Class, observing students to identify those with genuine potential. Unbeknownst to her at the start of the series, three of the main students—Akari, Yuki, and Nozomi—are the daughters from whom she was separated long ago. The story follows their journey as they uncover the truth of their shared past, leading to a final reunion where they reveal to her that they are her long-lost children.

Her key relationship is with her adopted daughter, Reika. While they share a close and loving bond, jealousy emerges on Reika's part when Kisaragi begins focusing her attention on new students. Kisaragi also has a long history with a man named Shiro, a songwriter who helped her and her husband in the past and who continues to support her as a coach at the music school. Over the course of the narrative, Kisaragi undergoes significant emotional development. She starts as a figure haunted by her past mistakes and losses, but through her interactions with the young singers and the eventual reunion with her biological children, she is able to confront her grief and find a measure of healing. Her notable abilities include her own prowess as a former singing star, but more importantly, her exceptional skill as a talent scout and mentor who can recognize raw potential and guide young artists toward success.