Kozue Matsumoto is a schoolmate of Baki Hanma and the daughter of his landlady, Kinuyo Matsumoto. Her father was an underground arena fighter who died in that brutal setting, a fact that later shapes her deep unease with Baki’s world. She first appears as a quietly caring neighbor, feeding Baki’s dog and bringing him dinners when he neglects school and normal life to train.

Her personality is initially reserved and somewhat shy, yet she reveals a more spirited and assertive side when the situation demands it. She is devoted to Baki but often denies her feelings when questioned, flustered by the intensity of what he does. She is profoundly disillusioned by the violence of underground fighting and repeatedly begs him to abandon that path, worried for his safety and troubled by the suffering he endures and inflicts. Despite this, she is not passive; she confronts Kaoru Hanayama when he dismisses her importance to Baki’s life, telling him that fighters too often ignore the women who care about them. She also interposes herself between Baki and his father during their historic clash, scolding them for talking instead of fighting seriously, showing a strange fearlessness in the face of the world’s strongest beings.

Her motivation is rooted in a desire for Baki to be safe and for their relationship to exist apart from the brutal tournaments. While she initially wants him to quit, her view matures after visiting the grave of Emi Akezawa, Baki’s mother. There she begins to grasp the depth of his resolve and the burden of his lineage, shifting from simple disapproval to a more complex, resigned understanding. She comes to accept that his violence is inseparable from who he is, and she chooses to support him rather than flee.

Kozue plays the central role of Baki’s emotional anchor and love interest. She is a window into a normal life he otherwise lacks and a measure of his humanity. In the second series, their intimate relationship becomes a turning point: just before Baki’s fight with the convict Ryuukou Yanagi, they make love, an act that symbolically and literally allows Baki to become a “full man” and strengthens his resolve. She later aids his recovery from Yanagi’s poison, earning rare approval from Yujiro Hanma, who remarks that she is the best woman Baki could have. Throughout the narrative, she witnesses fights, offers silent support, and occasionally becomes a direct onlooker, such as when she is kidnapped by school thugs in an anime-only sequence that prompts Baki to rescue her.

Her key relationships orbit Baki and his family. She is the daughter of Kinuyo, the landlady who provides Baki a home. Her father’s death in the arena is a shadow over her feelings. With Baki, she shares a bond that endures despite his brutal career and the interference of Muhammad Alai Jr., who briefly complicates their connection. Yujiro Hanma, the feared ogre, acknowledges her worth after seeing her stand by Baki during his poisoning. She also interacts with fighters like Hanayama and the Shinogi brothers in passing, always as a concerned outsider peering into a world she can never fully join.

Over the course of the story, Kozue evolves from a nervous, peeking neighbor into a companion who comprehends the gravity of Baki’s choices. Her acceptance comes not without cost; she grows quieter and less present in later arcs, but her early active resistance and later steadfast presence mark her development. She possesses no fighting skills or physical abilities of note. Her strength is emotional: the courage to speak plainly to monsters, the patience to wait for someone who may not return, and the resilience to remain a soft center in a tale of extreme physical violence.