Kozue Otomune is a main character from the multimedia project Love Live! Hasu no Sora Jogakuin School Idol Club, which is part of the larger Love Live! franchise. She is a student at Hasunosora Girls' High School, where she is a member of the school's idol club and the sub-unit Cerise Bouquet. Her image color is a shade known as mermaid green, and her symbolic motif is a phonograph.

Born into a wealthy and deeply traditional family of musicians, Kozue was raised in an environment steeped in classical music and began learning various instruments from a very young age. Her family’s expectation was for her to become a refined musician of classical arts. However, her life path changed when she witnessed a performance by school idols as a child, which sparked a deep and abiding passion for this form of expression. This dream was initially met with strong opposition from her family, who did not consider school idols to be a legitimate art form. After much persuasion and setting certain conditions, Kozue was eventually able to gain their understanding and permission to pursue her ambition, leading her to enroll at Hasunosora, a school with its own history of school idol activity. Her ultimate goal is to win the Love Live! competition, a victory she feels would validate her choices and sacrifices.

In terms of personality, Kozue is the quintessential elegant and graceful honor student, excelling in both academics and athletics. Despite being widely admired and respected by her peers for her talents and looks, she is never boastful or complacent. She is a diligent and earnest individual who puts maximum effort into every endeavor. One of her most notable traits is her perfectionism, though it is a standard she applies almost exclusively to herself. She sets extremely high and precise goals for her own performance and has a tendency to be self-blaming when things do not go as planned. While she usually presents a calm and formal demeanor, always speaking politely and using honorifics, she does possess a hidden temper. Her close friend Tsuzuri Yugiri has mentioned that she and Kozue used to have frequent shouting matches in their first year, hinting at a fiercer, more passionate side beneath her polished surface. A running gag is her notorious struggle with modern technology, particularly smartphones and other devices, though she insists she is gradually improving. Her hobbies include stargazing, listening to music, and making tea cakes, and her special skills are classical ballet and strength training.

Kozue serves a pivotal role within the story, primarily as the president of the Hasunosora Girls' High School Idol Club, with many believing there would be no club without her. Her key relationships are central to the narrative. She forms a close partnership with her junior, Kaho Hinoshita, as the two are the members of the duo unit Cerise Bouquet. Kozue acts as a mentor to Kaho, and their bond deepens over time, to the point where Kozue eventually drops the formal honorific when addressing her. Her other vital relationships are with her classmates, Tsuzuri Yugiri and Megumi Fujishima. As first-year students, the three were known as the "Hasu Trio." However, this period was marked by significant friction due to their strong personalities, leading to arguments and a painful falling out that caused them to disband and vow not to perform together again. This past conflict is a major source of drama and character development.

Kozue's character undergoes considerable development throughout the timeline. As a first-year, she is described as rigid, strict, and overly focused on winning, to the detriment of her relationships. After a falling out with her peers, she becomes more guarded. Her growth is spurred by her interactions with the new first-years, particularly Kaho, when Kozue becomes a second-year. Through her partnership with Kaho and a series of events leading up to a school festival, she is able to reconcile with Tsuzuri and Megumi, resolving their past issues and learning to be more open and honest about her feelings rather than hiding behind a facade of perfection. A significant moment in her development occurs after a loss at the national tournament, where she is found crying alone in the club room by Kaho. This moment of vulnerability allows her to accept support and reaffirm her commitment to achieving her dreams together with her friends, not in isolation. She eventually graduates and goes on to study music at a university.

Kozue possesses a wide array of notable abilities, most stemming from her rigorous musical upbringing. She can play a vast number of instruments, including the piano, violin, trumpet, flute, saxophone, and acoustic guitar. She also uses these skills to compose original songs for her unit and the club. Beyond music, she is an accomplished athlete, with classical ballet training and a surprising amount of physical strength, once easily lifting up her partner Kaho. Despite her many talents, she has a notable weakness in visual arts, as her drawings are famously unskilled, though she has shown slight improvement over time. Her favorite phrase, "Stand like a peony, sit like a peony, walk like a lily," is a classical Japanese saying that describes the ideal graceful demeanor of a beautiful woman, a principle she embodies in her own conduct.