The game was a departure from Square's standard role-playing games, introducing a substantial action-adventure element to the gameplay.Kingdom Hearts has an all-star voice cast and includes many of the Disney characters' official voice actors. It was longtime Square character designer Tetsuya Nomura's first time in a directorial position.
Kingdom Hearts was praised for its unusual combination of action and role-playing, as well as its unexpectedly harmonious mix of Square and Disney elements. It was a dominating presence in the 2002 holiday season, receiving numerous year-end "Best" video game awards, and went on to achieve Sony's Greatest Hits status. Since its release, Kingdom Hearts has sold over 5.6 million copies worldwide and has prompted numerous sequels. Kingdom Hearts is currently the ninth best selling PS2 game of all time and the most commercially successful entry in the series to date.
Kingdom Hearts begins on Destiny Islands, where Sora and his two childhood best friends; Riku & Kairi live. The three friends want to leave the islands to explore new worlds and have prepared a raft for this purpose. One night, the islands are attacked by shadow creatures—the Heartless. Sora seeks out his friends, finding Riku, who disappears into a dark portal. At the same time, Sora obtains the Keyblade, a weapon effective against the Heartless. However, the islands are destroyed and Sora drifts into space. Meanwhile, King Mickey has left his own world to deal with the increasing numbers of Heartless and left instructions for Donald and Goofy to find the "key" that will protect the worlds from the encroaching darkness.
Donald and Goofy use the Gummi Ship to reach Traverse Town, where Sora has drifted. Sora meets Leon, who explains that the Heartless are beings that consume hearts, and that the Keyblade is the only weapon capable of defeating them. A man named Ansem is said to have studied the Heartless. Sora then meets Donald and Goofy, and the three decide to travel together—Donald and Goofy to find King Mickey, and Sora to find Kairi and Riku. The three go to various worlds based on Disney films, finding that the Keyblade also locks "Keyholes", passages to the "heart" of a world which, when sealed, prevent it from being consumed by the Heartless. Meanwhile, a group of Disney villains, led by Maleficent, seek out the seven Princesses of the Heart to unlock the final Keyhole that leads to "Kingdom Hearts", a repository of knowledge and power and the source of all hearts. This group includes Riku; Maleficent promises that she will help him find Kairi in exchange for his support. Maleficent sows distrust in Riku, telling him that Sora abandoned him and Kairi for new friends and the Keyblade. An increasingly antagonistic Riku finds Kairi's body, but cannot find her heart.
Sora and his friends eventually arrive at Hollow Bastion, Ansem's home world and Maleficent's current headquarters. Riku takes the Keyblade from Sora, claiming to be the true Keyblade master and that Sora only received it in his absence. Donald and Goofy, having been explicitly ordered to follow the "key", reluctantly leave Sora for Riku. Sora challenges Riku, stating that his heart derives strength from his friends; his friends return to him, as does the Keyblade. Shamed, Riku meets a cloaked man who goads him to give into the darkness. Meanwhile, the three engage and defeat Maleficent. Sora finds Kairi's body and confronts Riku, who reveals that he is possessed by Ansem. Ansem explains that Kairi is a Princess of Heart, and that her heart has been hiding within Sora's body since Destiny Islands was destroyed. After defeating Ansem, Sora impales himself with Ansem's Keyblade, releasing both his and Kairi's heart. Kairi's heart returns to her body, in turn completing the final Keyhole, while Sora becomes a Heartless. Kairi recognizes Sora's Heartless and the light in her heart restores him to human form. He resolves to confront Ansem.
Ansem is found in End of the World, the combined remnants of worlds taken by the Heartless. Ansem seeks Kingdom Hearts, hypothesizing it to be the ultimate darkness. Upon opening the door to Kingdom Hearts, however, it reveals its light, overwhelming and destroying Ansem. Beyond the door are King Mickey and Riku, and they help Sora and the others close the door, as there are many Heartless beyond it. Mickey and Sora use their Keyblades to lock the door. The worlds lost to the Heartless reconstruct themselves; as the Destiny Islands reform, Kairi returns there while Sora is forced to part with her. The game concludes as Sora, Donald, and Goofy resolve to find Riku and Mickey.
- Originally, Sora was not the main charcter, as Disney wanted Donald Duck to be the main character while Square wanted Mickey Mouse to be the main character. Because of this, Tetsuya Nomura created Sora, while having Mickey Mouse in mind. He was also going to have a chainsaw-like blade instead of the keyblade, but Disney did not approve. He also was going to have a tail, but was removed because it looked similar to Final Fantasy XI's Zidane Tribal, who also had a tail.
- The Disney characters in the Game all have their original voice actors. (Except for the ones that passed away before Kingdom Hearts)
- Kingdom Hearts was originally going to have a much more simpler, Disney oriented storyline, but it was changed to make it appeal to Final Fantasy fans.
- The main theme, Simple and Clean, is sung by Utada Hikaru. The instrumental to the song is based off of Hikaru's: "Hikari"
- In Japan, a second version of Kingdom Hearts exist's known as: "Kingdom Hearts Final Mix", this version included several events and a number of gameplay tweaks that are not in previous releases. Spoken dialogue is in English, with Japanese subtitles. New scenes, clarifying certain plot points, such as Riku's journey and foreshadowing of Kingdom Hearts II, were included. A gameplay option allows the player to skip cut scenes after seeing them once.The optional bosses first included in the English version were introduced to Japanese players for the first time, along with a new fight against "Unknown Man", in an attempt to raise interest for the sequel. Kingdom Hearts HD 1.5 Remix, includes this version of the game.
- The idea for this game came about when producer Shinji Hashimoto met with a Disney executive in an elevator; Square and Disney had previously worked in the same building in Japan.
- This was Squaresoft's last game before the Square and Enix merger.
- Before the game was released in the U.S., Square held a "Name-in-Game" contest. A person named Kurt Zisa won the contest, and his name was used for a hidden boss in the game.
- Sora, Riku, and Kairi are named after the three primary elements of nature. In Japanese, riku means 'land', kai means 'ocean', and sora means 'sky'. the name Kairi could originate from the Japanese word "hikari", which means light, because she is the only untainted main character. "Hikari" is the Japanese version of "Simple and Clean," though the lyrics have an entirely different meaning.