Impactor Logia is the commander of the Impactor unit, a group sent to Earth on a mission of annihilation. His background lies with the Cosmic Alliance, which entrusted him with the task of destroying humanity at all costs, an order he initially follows with a strict sense of honor and duty. To execute this plan, he adopts the human guise of Shuichi Yoshihama, infiltrating society by posing as an assistant to a professor named Wakui. His primary objective during this time is to gain control of a powerful mecha called Guntras to trigger a solar supernova, which would wipe out the Earth.

Logia possesses a cunning and astute personality that distinguishes him from more conventional adversaries. He is highly strategic, often preferring to work from the shadows and manipulate events rather than engage in direct confrontation, leaving the frontline battles to his subordinates while he orchestrates larger schemes. When his carefully laid plans fail, his obsessive and determined nature intensifies, transforming into a relentless drive for revenge against the Gransazers who thwarted him. Despite his villainous role, he is characterized by a strong personal code of pride, which ultimately prevents him from taking dishonorable actions. His core motivations evolve over time; while he begins as a loyal soldier following orders to destroy Earth, his failures and personal losses shift his focus toward vengeance and a personal rivalry with the Gransazers, particularly with the protagonist Tenma.

In the narrative, Logia serves as the most persistent and formidable foe of the Gransazers, acting as a major antagonist. After a critical early plan fails, he disobeys his superiors' orders to retreat and remains on Earth, launching a series of intricate and desperate schemes to eliminate his enemies one by one. His role is complex, as he is not simply a monster of the week but a recurring nemesis who commands his own giant robot, Dailogian, to fight the heroes’ mecha on equal footing. Key relationships define his arc. He shares a deep bond with his fellow Impactors, particularly Lucia, for whom he harbors feelings; he once jeopardized his mission to save her life. His relationship with Tenma is central, beginning as a purely antagonistic one but deepening into a mutual rivalry and a grudging respect. He also has a strained relationship with his own higher authority, as he is eventually manipulated and betrayed by his superior, Belzeus, who reveals himself to be the true mastermind behind many of the characters' suffering.

Logia undergoes significant development throughout the series. He starts as a loyal and cold commander but evolves into a rogue agent driven by personal vengeance. A pivotal moment occurs when he attempts to self-destruct to kill his enemies; at the last second, he saves Tenma, realizing such an act would violate his pride as an Impactor warrior. Later, after being betrayed and stripped of his power by Belzeus, his role shifts once more. He refuses to give up, reclaims his mecha, and eventually sets aside his feud to ally with the Gransazers against their common enemy. At the story's conclusion, he resolves his rivalry with a final fistfight that ends in a draw, accepts that he is tired of fighting, and departs to face whatever judgment awaits him, having evolved from a genocidal commander to a complex anti-hero.

Notable abilities include his transformation into his Impactor form, where he wields a pistol-like weapon called the Hiro-Sniper. Like other members of his species, he is a skilled hand-to-hand combatant. His most significant asset is his command of the giant mecha Dailogian, which he summons to battle the Gransazers' own colossal war machines.