The youngest and newest member of the Organization, Roxas, was found in Twilight Town by Xemnas. He is also referred to as the "Key of Destiny". Roxas's original self is Sora. He is voiced by Jesse McCartney in the English version of Kingdom Hearts II and Koki Uchiyama in the Japanese version. When pre-release Kingdom Hearts II screenshots and video showed this character without an Organization coat, he was featured prominently, emphasizing his importance to the future game's plot. In battle, he uses the "Oathkeeper" and "Oblivion" Keyblades, which represent Sora's memories of Kairi and Riku, as well as the power of light. As a stronger Nobody, Roxas controls Samurai Nobodies. Roxas's backstory and his joining of Organization XIII itself will be explored in the upcoming Kingdom Hearts 358/2 Days, for the Nintendo DS. Roxas will be a playable character in the game.

Unlike the other Organization members, Roxas lacks memories of his previous life, due to the short time Sora had spent as a Heartless. During Roxas's time in the Organization, he and Axel became friends, but Roxas leaves to find answers as to why he possesses the Keyblade. He is confronted by Riku, who defeats Roxas and takes him to DiZ. In Kingdom Hearts II, DiZ places Roxas in a virtual Twilight Town, leaving him without any memory of the Organization and with a fabricated identity to throw them off. While here Roxas begins seeing his other self's memories in dreams. Roxas lives an otherwise normal life in "Twilight Town" until Axel infiltrates it to save him. Despite Axel's attempts to stop him and Roxas gaining back his memories of the Organization, Roxas merges with Sora early in the game, which also causes some of Roxas's memories to influence Sora.

Roxas appears twice more later in the game. The first is a battle with Sora, shown only as a cut scene and never fully explained. In Kingdom Hearts II Final Mix, Sora's battle with Roxas is made playable, and a cut scene is added that shows Xemnas explaining that Axel's death triggered the reappearance of Roxas. Roxas appears once again with Naminé before Kairi enters the corridor of darkness back to Destiny Islands. He and Naminé imply that they will live on within Sora and Kairi as both a part of them and as individuals, as seen in the ending cinematic when they smile at each other through Sora and Kairi.