Makuba is the younger brother of Seto Kaiba. He is a loyal and devoted child who supports his brother unconditionally, often acting as a moral compass when Seto's ruthless ambition goes too far. Makuba is not afraid to question Seto when he believes his brother is making a mistake, and he challenges anyone who speaks ill of Seto. Despite his youth, Makuba is intelligent and knowledgeable about computers and business; he serves as vice president of KaibaCorp and once devised a plan to protect the company's reputation. His personality is kind‑hearted and somewhat naive about the wider world, but he is also spunky and shares his brother's love for games. Makuba's primary motivation is to see Seto smile again, remembering that after their difficult childhood in an orphanage, Seto's smile faded when he had to become ruthless to run the company.

In Yu‑Gi‑Oh!: The Movie (Pyramid of Light), Makuba appears as a supporting character. He is the one who brings Yugi and his friends to Kaiba's Duel Dome after the mysterious events at the museum. During the climactic duel between Seto and Yami Yugi, Makuba is present in the dome; when the pyramid manifests and the building begins to crumble, he flees to safety. Later, Maximillion Pegasus arrives in a helicopter and rescues Makuba along with Tea and Solomon. Makuba does not duel in the movie and possesses no supernatural abilities. His notable qualities are his loyalty, his technological savvy, and his unwavering faith in his brother. He is the only person Seto consistently cares about more than anything else, and their bond is the emotional foundation that humanizes Seto. Throughout the story, Makuba's role is to support his brother and to act as a link between Seto and the other characters, ultimately departing with Seto at the end after his brother promises to defeat Yugi another day.