Kim Hotaru is a supporting character in RahXephon who serves as a regular operator for the organization TERRA. She holds Australian nationality and is of Korean descent, and her most defining characteristic is the deep, unhealed wound left by the loss of her parents. When she was a child, they were killed during a devastating attack on an Australian city by a Dolem, a monstrous being from the otherworldly Mu. This tragic event is the single most important factor shaping her identity and her entire reason for being.

On the surface, Kim often presents herself as sharp-tongued, aggressive, and driven by a fierce sense of purpose. This is most apparent in her early interactions with the protagonist, Ayato Kamina. Frustrated by his initial refusal to pilot the giant mecha RahXephon, she harshly criticizes him, channeling her pent-up anger and desire for vengeance against the Mu onto him. Underneath this hardened exterior, however, lies a deeply caring and vulnerable person. She shares a close bond with Megumi Shitou, whom she considers her best friend, and is involved in a secret romantic relationship with their superior officer, Souichi Yagumo. She keeps this relationship hidden, partly out of a sense of guilt and a desire not to hurt Megumi, who also has feelings for Yagumo. When Megumi discovers the truth, Kim breaks down, revealing the depth of her care for her friend and her remorse for the deception.

Within the story, Kim's primary motivation is revenge. Her job at TERRA is not just a career but a personal crusade to combat the Dolems and the Mu, hoping to avenge her parents' deaths. This drive places her in direct contrast with Ayato, who is initially reluctant to fight. Her role often serves to highlight the human cost of the conflict and the raw, traumatic emotions that drive people to war. As the series progresses, Kim's development is a poignant exploration of how a person is marked by childhood trauma. Her internal state is visualized as a split between the determined young woman marching forward and the crying child she still is inside. She is forced to confront her pain directly when the same type of Dolem that killed her parents returns. Ayato, understanding her suffering but not sharing her lust for revenge, ultimately defeats the creature on her behalf, providing a form of closure she could not achieve on her own.

Key relationships heavily influence her development. Her secret romance with Yagumo provides a source of personal happiness and even leads to her becoming pregnant near the end of the series, an event hinted at by her suffering from morning sickness. This potential for a new life and a future stands in stark contrast to the death and loss that have defined her past. Her relationship with Megumi is complex, defined by friendship and the pain of secrets. In the series' final arc, Kim suffers another profound loss when Yagumo is killed, adding another layer of trauma to her already burdened psyche. Regarding notable abilities, Kim does not possess any supernatural powers or fight on the battlefield. Her talents are strictly non-combat; she is a skilled and intelligent TERRA operator, proficient in data analysis, tracking enemy movements, and performing her duties on the bridge. Her real strength lies in her emotional resilience, surviving profound loss and continuing to fight for a world she believes in, even as her motivations and relationships are tested to their limits.