Melon is a major antagonist introduced in the latter part of the story, serving as a formidable and deeply troubled adversary. He is a hybrid, born from a leopard mother and a gazelle father, which places him in a unique and socially fraught position within a world largely divided into carnivores and herbivores. His physical appearance is a direct blend of these two species, possessing the horns of a gazelle combined with the teeth, claws, and feline eyes of a leopard. To hide his carnivorous features and pass as a harmless herbivore in public, he frequently wears a surgical mask over his mouth and squints his eyes. His body is also marked by leopard spots that emerge as he ages, which he obsessively covers with intricate tattoos of melon leaves, a practice that also serves to infuse his life with a sense of pain and feeling.

Melon’s personality is defined by deep-seated psychological damage, cruelty, and a brilliant but twisted cunning. Under a veneer of affable charm and seemingly childlike curiosity, he is a ruthless, manipulative, and sadomasochistic individual. Having been bullied as a child for his mixed heritage, he grew up without a stable sense of belonging, belonging fully to neither the world of carnivores nor herbivores. This internal conflict is constant; he explains that when he sees herbivores, he feels an overwhelming urge to kill them, yet when carnivores approach, he is consumed with irrational fear. Adding to his alienation, his hybrid physiology has robbed him of his sense of taste, causing all food to seem like sand. As a result, he cannot derive pleasure from eating in the way other animals do, and he claims that the only way he can feel truly alive is through the experience of pain, such as that inflicted by his tattooing sessions. This pursuit of sensation extends to his actions as a serial killer, finding a grim excitement in the act of murder.

Melon’s motivations are not driven by simple goals like power or wealth but stem from his fractured identity and his hatred for the society that rejects him. He is bored with ordinary life and appears to take a cynical, mocking pleasure in exposing societal hypocrisy and the vulnerability of others. He seems to want to cause chaos and pain, both to others and himself, as a way to validate his own existence. As the boss of the Shishigumi, a lion mafia syndicate, he wields his authority with arbitrary cruelty, forcing his subordinates to subsist primarily on melons and meting out violent punishments for minor infractions, a stark contrast to the firm but fair leadership of his predecessor, Louis.

Within the story, Melon serves as a dark mirror to the protagonist, Legoshi. Both are hybrids, but while Legoshi struggles to reconcile his carnivorous nature with his gentle disposition and find love and acceptance, Melon has surrendered entirely to nihilism and hatred. Melon’s role is to embody the worst possible outcome of being an outcast. One of his most significant relationships is with the dwarf rabbit, Haru. When he meets her while working as a part-time university professor, he is unexpectedly fascinated by her, sensing in her a similar kind of "lightness" or disregard for her own safety. For the first time in his life, Melon experiences genuine appetite and desire, wanting to devour her not out of instinct but out of a newfound, twisted longing. This encounter shakes him profoundly, leading him to realize that he was capable of being hurt by another person’s rejection. His relationship with Legoshi is one of antagonism and a perverse sense of kinship. Melon mocks Legoshi for his empathy but is also intrigued by him, engaging in a cat-and-mouse game that forms the central conflict of the story's latter half.

Throughout his development, Melon is shown to be a product of a traumatic childhood. He committed his first murder at the age of nine, killing the bullies who tormented him. His mother, a leopard who decorated their home like a fairy tale, is implied to have held a deeply disturbed and potentially abusive affection for him, seeing the gazelle husband she presumably devoured in him. After learning that his name, Melon, was chosen because it is neither a fruit nor a vegetable but still considered delicious—a metaphor for his own existence—he killed his mother in a fit of rage. Despite his monstrous actions, he retains a trace of longing for a normal life and love, a vulnerability that is briefly exposed in his interactions with Haru and is ultimately what leads to his psychological unraveling. In the end, his body undergoes a dramatic transformation, becoming more muscular and covered in leopard spots, representing his final, uncontrollable shift toward his carnivorous side before his ultimate defeat and imprisonment, where he is last seen reading fan mail, an act that suggests a continued, warped desire for a form of connection.

In terms of abilities, Melon is highly intelligent and a master of psychological manipulation, using his disguise and understanding of animal psychology to deceive and murder, even posing as a therapist to target elephant patients for their ivory. He has a remarkable resistance to blood loss and physical trauma, continuing to fight and even shooting himself to prove a point about his hybrid resilience. His sadomasochistic nature means that inflicting pain on him often only makes him fight harder, removing any tactical advantage an opponent might gain from wounding him.