Claude, also known as Phantom Sword Claude, is a significant character in Concrete Revolutio who serves as a primary foil to the protagonist Jirou Hitoyoshi. He is a superhuman whose past is deeply intertwined with Jirou and Emi, as he appears to have known them since childhood, with visual cues suggesting he may have been the mysterious boy shown in an old photograph alongside a young Jirou.

Claude is characterized by a rigid and uncompromising moral code, believing that superhumans should exist to fight for what he defines as "freedom, peace, and justice". However, his methods are brutal and his worldview is starkly black-and-white. He categorizes other superhumans into simple labels of "good" or "bad," and he shows little regard for human life when he deems his victims to be on the wrong side of his personal morality. This is horrifically demonstrated when Kikko, who attempts to sympathize and negotiate with him, follows him to his home only to discover it is full of freshly murdered bodies. This extremist approach to justice positions him as a vigilante who commits evil acts in what he believes is the interest of a greater good.

His motivations are rooted in a deep disillusionment with systems of authority, particularly government and military institutions that exploit superhumans for their own ends. He is driven to expose these injustices, such as the dark secret of the American submarine Antares, which was designated as "superhuman" because it was powered through gruesome human experimentation. This mission puts him into direct conflict with the Superhuman Bureau, which he views as complicit or ineffective. He eventually kills the Bureau Chief, Akita, and takes the witch Kikko as his captive, actions that push the Bureau to its breaking point.

Claude's primary role in the narrative is to act as a dark mirror to Jirou. While Jirou struggles to find a middle ground and maintain his idealism in a world of moral grey areas, Claude has fully embraced a radical, violent path in service of his principles. He directly confronts Jirou, berating him for his idealism and forcing him to confront the consequences of his beliefs. Their personal history and ideological clash form the emotional core of a major turning point in the series, leading to a confrontation that showcases their similarities and differences while pushing Jirou to eventually leave the Superhuman Bureau.

In terms of abilities, Claude is a formidable combatant. He wields a sword and is known for devastating flame-based attacks that are visually similar to Jirou's own powers, though colored yellow instead of Jirou's flames. His influence extends beyond his own actions, as technology modeled on his mask is later developed, which appears capable of enhancing superhuman abilities or potentially inducing mind control in the wearer. His character develops from a mysterious masked antagonist into a symbol of violent rebellion, his actions catalyzing the widespread social and political conflicts between superhumans and the government as the series progresses.