Combatiente D is the central protagonist of the story, originally a low-ranking member of a monster army that invaded Earth. He belongs to a class of foot soldiers known as Dusters, who were created after the initial invasion. For over a decade, these monsters have been forced to participate in a staged, televised conflict where they are defeated by the Divine Dragon Rangers every Sunday for the entertainment of the public. This existence is a humiliating charade, as the war was effectively won by the Rangers within a year, leaving the surviving monsters as mere props.

His personality is defined by a deep-seated rebelliousness and an unyielding refusal to accept this subjugated role. Unlike his fellow Dusters, who have largely lost their will to fight, Combatiente D has not abandoned his original goal of conquering the world and destroying the Ranger force. He is characterized by his immense tenacity, improvisational skill, and a cautious yet daring nature. While he presents a hard and often arrogant exterior, driven by a selfish desire to win at any cost, he possesses a surprising capacity for empathy and a sense of fairness. He despises winning through underhanded means or outside help, as it violates his pride as a monster warrior. This pride even leads him to cry out for a fair fight against an enemy he respects. His understanding of human life and social norms is initially very limited, forcing him to learn about the world through observation, books, and radio.

Combatiente D's primary motivation is to dismantle the false system of the Divine Dragon Rangers from within and achieve true world domination. After being effortlessly defeated in a staged battle, he realizes that open rebellion is futile. Instead, he infiltrates the Ranger Force by taking a human disguise, eventually assuming the identity of a rookie candidate named Hibiki Sakurama. This infiltration marks the core of his role in the story, as he works as a mole, stealing divine artifacts and plotting the downfall of his oppressors.

Throughout his journey, he forges complex relationships with several key characters. He forms an uneasy alliance with Yumeko Suzukiri, a sadistic and ambitious Ranger from the Yellow Battalion who secretly shares his goal of destroying the Ranger Force. His relationship with Hibiki Sakurama is pivotal; Hibiki is an idealistic ranger candidate who believes in coexistence between humans and monsters. After a critical incident, Hibiki offers his own identity to D, allowing the monster to live his life for him while Hibiki disappears, creating a deep and complicated bond between them. D also has significant interactions with members of the Ranger Force, including the Green Keeper, Chidori, who sees D not just as a monster but as a young fighter, which forces D to reconsider his black-and-white view of his enemies. He also encounters the Invader Rights Association, a human group that claims to seek coexistence, leading to further moral complexity.

Combatiente D undergoes significant development from a single-minded agent of revenge to a more introspective character. His experiences among humans, his rivalries, and his uneasy alliances force him to confront his own sense of identity and justice, blurring the lines between monster and hero.

His notable abilities set him apart from a typical warrior. As a Duster, he possesses near-immortality; he can regenerate from most wounds, including being dismembered or blown apart, as long as his core remains intact. He can also disassemble and reconstruct his body at will, a skill he uses to survive attacks and even to reshape his limbs into weapons. Furthermore, he has a specialized mimicry ability that allows him to change his appearance to perfectly imitate specific humans, a skill that is crucial for his infiltration and is considered superior to that of his fellow monsters. Despite his cleverness and these unique powers, his raw combat strength is very poor compared to the Dragon Rangers, forcing him to rely on strategy, deception, and his immortality to survive.