Kingdom Hearts is a series of action role-playing games developed and published by Square Enix (originally by Square). It is a collaboration between Square Enix and Disney. Kingdom Hearts is a crossover between Square Enix and Disney based in a fictional universe. The series centers on the main character, Sora, and his journey and experiences with various Disney, Square Enix and Pixar characters. The heroes of the series clash against the multiple incarnations of the primary antagonist, Xehanort, throughout the series.
Kingdom Hearts is the first game in the series, released in Japan on March 28, 2002 for PlayStation 2. Tetsuya Nomura served as game director, his first time in this position. Kingdom Hearts introduced the main characters (Sora, Kairi and Riku) of the series, and established the plot's framework involving hearts and dark beings known as the Heartless. It also established the role of Disney characters in the series, with character cameos from the Final Fantasy series. Kingdom Hearts was released in North America on September 17, 2002, and featured additional content that was not in the original Japanese version. The game was later re-released in Japan as Kingdom Hearts Final Mix on December 26, 2002. Final Mix includes the content from the North American release and additional enemies, cutscenes, and weapons.
Kingdom Hearts: Chain of Memories is a direct sequel to the first game. It was released on the Game Boy Advance in Japan on November 11, 2004. Chain of Memories was touted as a bridge between the two PlayStation 2 titles, introducing and previewing plot elements that would be explored in the next game. The gameplay system is a departure from the original and employs card game mechanics in real time. Players construct decks out of cards that correspond to different actions in battle, such as attacking or using magic. It was remade into a PlayStation 2 game titled Kingdom Hearts Re:Chain of Memories, which contains polygonal graphics instead of the sprites used in the original game. 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.
Kingdom Hearts II takes place one year after the events of Chain of Memories. It was released for the PlayStation 2 in Japan on December 22, 2005. The game further explores the "heart" concept by involving a new group of enemies, the Nobodies, which are the cast-off shells of those who have become Heartless. The gameplay is similar to that of the first Kingdom Hearts game, with the addition of the Reaction Command, which performs context-sensitive actions in battle. Kingdom Hearts II was revised into Kingdom Hearts II Final Mix, which contains more material than the original release, such as additional cutscenes and bosses. Kingdom Hearts II Final Mix was released with Kingdom Hearts Re:Chain of Memories in a collection titled Kingdom Hearts II Final Mix+, which was released in Japan on March 29, 2007
Kingdom Hearts HD 2.5 Remix: After the announcement of HD 1.5 Remix, Nomura stated that it would be "pretty unnatural" if Kingdom Hearts II did not receive an HD update. In the credits of HD 1.5 Remix, clips of Kingdom Hearts II Final Mix, Kingdom Hearts Birth by Sleep Final Mix and Kingdom Hearts Re:coded were shown, hinting at another collection. 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 1.5 Remix. The collection was released in Japan on October 2, 2014, North America on December 2, 2014, Australia on December 4, 2014, and Europe on December 5, 2014.