The series' legal ownership has long been debated amongst fans; this is because the game features Disney characters, but is created and primarily promoted by Square Enix, as well as featuring cameos by characters from the latter's franchises.

At the top of the castle, Sora and his friends battle Xemnas, who uses the remnants of Kingdom Hearts to fight them. Ansem, with few of his memories remaining, fills Aqua in about his experiences with Sora, which brings Aqua to tears of joy, knowing Sora will come and rescue her and her friends. Kingdom Hearts Integrum Masterpiece for Cloud: This bundle contains cloud versions of Kingdom Hearts HD 1. For Kingdom Hearts II, they released two versions, a standard version and a limited edition version. In addition to similar systems inherited from Birth by Sleep, this game features Dream Eaters which serve as both enemies and allies.

On October 14, 2013, the collection was announced for the PlayStation 3, and included the previously mentioned games, with Re:coded appearing as HD cinematics, similar to 358/2 Days in HD 1. Master Xehanort uses his replicas to wear down Sora, Donald, and Goofy; dons a new Keyblade armor, warping the world to help him fight; summons the X-blade in one final attempt to defeat Sora. The inclusion of specific Final Fantasy characters was based on the opinions of fans and the development staff.

As Master Xehanort moves in to turn Sora into the thirteenth and final vessel for the Organization, Lea, Donald, and Goofy arrive to aid Riku and Mickey, and Master Xehanort is forced to retreat with Young Xehanort, Ansem, Xemnas, Xigbar, Saïx, and his six hooded vessels. The first series, Kingdom Hearts, was broken up into four volumes, while the second series, Kingdom Hearts: Chain of Memories, was broken up into two volumes. The game further explores the "heart" concept by involving a new group of enemies, the Nobodies, which are the cast-off shells of the Heartless.The two main themes are Hikari, from Kingdom Hearts, Chain of Memories, Birth by Sleep and re:coded" and Passion, from Kingdom Hearts II and 385/2 Days. The remake was released in Japan as a second disc packaged with Kingdom Hearts II Final Mix on March 29, 2007, and in North America as a standalone title on December 2, 2008. Though they eventually defeat Maleficent, the three discover that Ansem, who has succumbed to the darkness, is the true mastermind. Gummi Ships are another common element of the series, which serve as the main mode of transportation between worlds in the games.