Claude, known as Nakajima in the original Japanese version, is a supporting character in the anime series. He serves as a loyal and efficient aide to Declan Akaba, the president of the Leo Corporation, a major organization in the story. Physically, Claude is a stocky man with fair skin. He has black hair styled with four distinct grey bangs at the front and wears a pair of blue-lensed hexagonal glasses. His typical attire is a professional grey business suit paired with a blue tie, fitting his corporate role.

In his capacity as an employee of the Leo Corporation, Claude acts as an assistant, analyst, and overseer of operations. His primary function is to handle logistical matters, collect data, and implement the directives of his superior, Declan Akaba. He is often found in the corporation's high-tech control room, monitoring Duels through surveillance systems, tracking the appearance of new summoning methods like Pendulum Summoning, and analyzing data from Duel energy readings. He also serves as a gatekeeper of sorts, managing access to Declan and attempting to control the flow of information and personnel within the corporation.

Personality-wise, Claude is professional and serious about his duties. He is often seen carrying out orders with little complaint, though he does express unease or concern in certain situations. For instance, he shows irritation when the Xyz Duelist Shay Obsidian refuses to use a Pendulum Card developed for him and is horrified when senior Duelists are easily defeated by invaders from another dimension, desperately proposing to send in a top team as a countermeasure. Despite these reactions, he remains deferential to Declan, trusting his judgment even when his own suggestions are overruled. His main motivation is the successful execution of his job and, by extension, the goals of the Leo Corporation.

Claude's role in the story is that of a background operator and exposition provider. He is not a Duelist and does not participate in any card battles. Instead, he contributes to the plot by informing the main characters and the audience of events happening off-screen, such as the detection of Synchro or Fusion Summoning in unexpected places, the status of tournament brackets, or the aftermath of attacks. He is involved in several key incidents behind the scenes, including orchestrating the theft of Yuya Sakaki's Pendulum cards early in the series and later attempting to manage the security crisis caused by the invasion of Duelists from the Fusion Dimension during the Arc League Championship tournament.

His most significant relationships are with the Akaba family. He works directly under Declan Akaba, taking orders from him and providing him with regular reports and analysis. He also interacts with Declan's mother, Henrietta Akaba, and is present for key strategic discussions with her. In the final arc of the series, he is shown assisting in the care of Riley Akaba, who has been transformed into a baby. Alongside Declan and Henrietta, Claude is seen gently rocking Riley in a cradle, indicating a degree of trust and proximity to the family's private affairs.

Claude shows very little personal development over the course of the series. He remains a consistent figure as Declan's aide from his first appearance to his last. His narrative function is stable, and his personality does not undergo any dramatic shifts. Notably, during the climax of the series, he is among the group of observers who watch the final Duels, learning about the fears and internal struggles of the protagonist, Yuya Sakaki, but remaining a spectator to the resolution of the conflict.

As a non-Duelist, Claude has no notable Dueling abilities, strategies, or signature cards. His skills are entirely administrative, technical, and logistical. He is proficient in using the Leo Corporation's sophisticated monitoring technology, managing security protocols, and discreetly handling operations such as bribing individuals with rare cards to ensure their cooperation.