Roxas' first appearances were cameos in "Another Side, Another Story", a bonus trailer found in Kingdom Hearts, and in the ending of Kingdom Hearts: Chain of Memories. In Kingdom Hearts II, Roxas is introduced as a kid living in a digital replica of a city called Twilight Town. Unaware of the virtual nature of the city, Roxas begins to dream about the adventures of Sora, the series' protagonist.[2] He later encounters Axel, a member of Organization XIII who was given orders to either rescue or kill him,[3] and Naminé, a special Nobody fighting against Organization XIII, who tells him he is Sora's other half.[4] Eventually, Ansem the Wise, the creator of the virtual world, leads Roxas to an old mansion where he sees Sora's comrades, Donald Duck and Goofy, sleeping in suspended animation.[5] It is then revealed that Ansem had placed Roxas in the replica of Twilight Town, erased his memory, and implanted false ones to make Roxas unaware of his past and then make him merge with Sora.[6] When he reaches the room where Sora is kept asleep, Roxas rejoins with Sora, allowing Sora to wake up.[7] Sora later learns that Roxas is his Nobody, created during the first game. Xemnas brought Roxas to Organization XIII as he could wield the Keyblade, a weapon which would help them to capture hearts. Roxas later betrayed the organization, and encountered one of Sora's friends, Riku, who captured him to help Sora wake up.[8] Roxas makes two appearances near the end of the game. The first is in a mental battle with Sora depicted as a cut-scene,[9] and the second is with Naminé who has merged with her other self, Kairi.[10] In the re-released version of the title (Kingdom Hearts II Final Mix), Roxas' fight against Sora was expanded, making him a boss character. The battle was meant to be interactive in Kingdom Hearts II, but time constraints imposed from creating fights for the other Organization XIII members prevented inclusion.[11] With the opportunity to include the fight, Nomura's team worked hard to make it entertaining for players.[1] Additional scenes regarding Roxas' past were added to the game to add to the mystery around him.[12]

Kingdom Hearts 358/2 Days, a prequel to Kingdom Hearts II, reveals Roxas' life with Organization XIII. Unlike the other Organization members, Roxas lacks memories of his previous life.[13] During Roxas' time in the Organization, he is placed under Axel's watch, and the two eventually become friends.[14] After Axel is sent to Castle Oblivion, Roxas is entrusted with Xion, another Keyblade wielder, whom he befriends before he falls into a month-long coma at the same time Naminé begins to restore Sora's memory.[15] Awakening and attempting to spend time with his friends, Roxas begins to react to Sora's memory restoration as he starts to question why he uses the Keyblade and doubt the Organization's motives. When he discovers that Xion is a replica of Sora created by Xemnas,[16] Roxas feels betrayed by Axel hiding this from him, and is compelled to defect from Organization XIII to find answers and meet Sora.[17] After doing so, he encounters Xion, who tries to attack and absorb him so that she would become the "real" Sora;[18] however, Xion allows Roxas to kill her in battle.[19] The death of his friend, coupled with full knowledge of how deranged Xemnas truly is, makes Roxas decide to defeat Xemnas and release the hearts he and Xion captured for the Organization.[20] On his way, Roxas is confronted by Riku who knocks him unconscious in order to help Ansem and Naminé wake up Sora.[21] A Pinocchio's chapter in the story was intended to add a sad mission focusing on Roxas and Xion "looking for hope for themselves" but such story was not added due to system-constraints.[22]

A virtual representation of Roxas appears as a boss character in the mobile phone game Kingdom Hearts coded, in which he confronts a virtual representation of Sora.[23] He makes a cameo appearance at the end of Kingdom Hearts Birth by Sleep, where he is shown with Xion and Axel eating sea-salt ice cream in Twilight Town.[24] Roxas also appears in Shiro Amano's manga and Tomoko Kanemaki's novels, which reprise his role in the video games.[25][26] The book Kingdom Hearts: Another Report includes a novel called Roxas–Somewhere in Time that retells Roxas' days in the Organization with the exception of his befriending Xion.[27] Roxas (ロクサス, Rokusasu?) is the Nobody of Sora.[52] The character's voice actors are Koki Uchiyama and Jesse McCartney in Japanese and English respectively.[11][13] Xemnas found him in Twilight Town and gave him the epithet, "Key of Destiny" (めぐりあう鍵, Meguriau Kagi?, lit. "Serendipitous Key"), using him to gather hearts for the Organization. Prior to the release of Kingdom Hearts II, screenshots and video showed Roxas without an Organization coat, in a black outfit with a white jacket and light brown pants. Roxas controls Samurai Nobodies and initially uses the Kingdom Key, the initial Keyblade, in battle. He can manipulate the power of light to augment his physical attacks and create energy-based melee weapons and barriers.[7] After Xion's sacrifice, Roxas inherits her Kingdom Key and turns both his and her Keyblades respectively into Oblivion and Oathkeeper, which both symbolize Sora's bond to Riku and Kairi and Roxas's promise to Xion to free Kingdom Hearts.[53] Roxas' backstory and his joining of Organization XIII were further explored in Kingdom Hearts 358/2 Days.[54] Roxas first appeared in "Another Side, Another Story", a bonus trailer found in Kingdom Hearts, and is mentioned in several cryptic comments made by other Organization members in Chain of Memories.