Riku (リク?) is Sora's and Kairi's best friend, and character created by Tetsuya Nomura for the Kingdom Hearts series. Nomura has stated that Riku's name can be interpreted as "land"; the Japanese on 'yomi pronunciation of land is riku (陸?).Riku is voiced by Mamoru Miyano in the Japanese version and by David Gallagher in the English version. As a child in Kingdom Hearts Birth by Sleep, he is voiced by Eiji Shima in the Japanese version. He is playable in the second story mode of Kingdom Hearts: Chain of Memories and as a world-specific ally in Kingdom Hearts II. In 358/2 Days, Riku is playable in the multiplayer mode and also serves as the final boss in the game's story mode.
Appearing in Birth by Sleep, Riku had an obsession to see other worlds and explained his reasons to Terra that he wanted to get stronger. He then held Terra's Keyblade at his request before Sora arrived and Riku promised not to tell him what occurred. By the beginning of the main series, now fifteen years old, Riku's desire was able to come true thanks to Kairi. Riku went with the darkness as their world is attacked by the Heartless, with the Keyblade coming to Sora. Separated from his friends, Riku ends up at Hollow Bastion where Maleficent finds him, thus giving him the Soul Eater. Under her influence, Riku turns on Sora and searches for a way to help Kairi. Riku eventually becomes possessed by Xehanort's Heartless, with his heart sent to the realm of darkness where he meets King Mickey and helps him and Sora seal the door to the realm of darkness.
In Chain of Memories, through DiZ, Riku awakens in the basement levels of Castle Oblivion and begins climbing to the ground floor. Along the way, Riku confronts the remaining darkness in his heart and a replica of himself that is created by Vexen; he also encounters DiZ, who has been overseeing his progress. After being reunited with King Mickey, Riku reaches the main floor where he finds Naminé as she attends to a sleeping Sora. She offers to seal away his darkness by sealing his memories, but Riku turns her down and chooses to find a balance between his light and darkness, allowing him to defeat what remained of Xehanort's Heartless. Soon after, donning the black cloak DiZ gives him along with a blindfold, Riku joins him to ensure Sora is restored in peace.
While capturing Roxas in order to make Sora complete again, Riku uses the power of darkness at the cost of becoming a physical manifestation of Xehanort's Heartless. Trapped in that form even after leaving DiZ, Riku helps Sora in secret, ashamed of his appearance and gaining the Way to the Dawn (ウェイトゥザドーン?) Keyblade. Riku returns to his original form when Ansem the Wise's machine to digitally seal away Kingdom Hearts malfunctions and self-destructs. Joining Sora, they battle and defeat Xemnas, however in his final maneuver, Riku is severely injured saving Sora. In the end, they end up on a dark beach, and discuss how strong their friendship is and how much each of them wanted to be like the other. Shortly after, a bottle washes ashore, Riku opens the bottle revealing the letter Kairi had written and hands it to Sora, saying it's for him. Sora reads the letter, thus opening the door to light, which leads them to Destiny Islands. The two use the portal to return home, but a while later, Riku bids farewell to Sora as the latter embarks on a quest to find and rescue Terra, Aqua and Ven from their individual fates.