Kingdom Hearts was a departure from Square's standard role-playing games by introducing a substantial action-adventure element to the gameplay. In addition, it has an all-star voice cast which included many of the Disney characters' official voice actors. Kingdom Hearts was longtime Square character designer Tetsuya Nomura's first time in a directorial position.
The game was praised for its unusual combination of action and role-playing, as well as its unexpectedly harmonious mix of Square and Disney elements. It received numerous year-end "Best" video game awards, was a dominating presence in the 2002 holiday season, and went on to achieve Sony "Greatest Hits" status. Since its release, Kingdom Hearts has sold over 5.6 million copies worldwide and has been followed by two sequels. Three more titles are currently being developed, which have a connection to a future, unannounced game.
Kingdom Hearts is influenced by its parent franchise, Final Fantasy, and carries gameplay elements over into its own action-based, hack and slash system. The main battle party consists of three characters: Sora, Donald Duck and Goofy. Sora is directly controlled by the player from a third person camera angle. All other party members are computer-controlled, though the player can customize their behavior to an extent through the pause menu. Donald and Goofy are the computer-controlled characters that are usable in most areas; nearly every world in the game features its own party member who can be chosen to replace Goofy or Donald in the party while the party is in that world. For instance, Jack Skellington can join the player's party in Halloween Town, but can not accompany the player elsewhere. On some worlds, the party changes its appearance, has abilities unique to that world, or both. For example, the party can fly in Never Land and has aquatic forms in Atlantica, which enable them to survive underwater.
Like many traditional role-playing games, Kingdom Hearts features an experience point system which determines character development. As enemies are defeated, the player gains experience which can lead up to a "level up", where the characters grow stronger and gain access to new abilities. Unlike other games of its type, Kingdom Hearts allows a certain degree of character development customization through a short tutorial found at the beginning of the game. The tutorial allows the player to select from one of three main attributes―strength, defense, and magic―for Sora to excel in and one to lack in. By choosing certain options, the player is able to manipulate how Sora learns abilities, grows statistically, and even gains levels. Donald, Goofy, and any other additional party members are assigned specific areas of strength from the outset. Donald excels in magic and Goofy excels in defense and special attacks.
The game is driven in a primarily linear progression to the next story event, usually told in the form of a cut scene, though there are numerous side quests available that provide bonus benefits to the characters. Most of the gameplay occurs on interconnected field maps where battles take place. Combat in Kingdom Hearts is in real time and involves pressing buttons to initiate attacks by the on-screen character. A role-playing game menu, similar to those found in Final Fantasy games, found at the bottom left of the screen provides other combat options such as using magic and items. There is also a context-sensitive option at the bottom of the menu, usually used for interacting with the environment or performing special attacks. This menu is manipulated by using the right analog stick or digital pad, while movement is controlled by the left analog stick, allowing the player to navigate the menu while avoiding or approaching enemies.
Each world varies in appearance and setting, depending on the Disney world upon which it is based. The graphics of the world and characters were meant to resemble the artwork style of the environments and characters from their respective Disney film. Each Disney world is inhabited by characters from their respective Disney film; Hercules and Philoctetes inhabit Olympus Coliseum, and Aladdin, Princess Jasmine, and Jafar inhabit Agrabah. Each world is disconnected from the others and exists separately. Most characters in the worlds are unaware of the existence of the other worlds, with the exception of some notable ones. Players travel from one world to another via Gummi Ship.
The worlds created specifically for the game mirror the overall appearance of the other worlds and feature either new characters or characters from several Final Fantasy games. The new worlds include: Destiny Islands, where the story initially begins; Traverse Town, which serves as a launching point for most of the game; Hollow Bastion, which many of the Final Fantasy characters call home; and End of the World, a large, dark world created from the remnants of various worlds consumed by the darkness. The main characters travel from world to world to seal each "Keyhole"; this protects the world from the Heartless and ultimately from destruction. They also try to minimize their interaction with characters of other worlds to maintain a balance of separation. This sometimes requires Sora, Donald, and Goofy to blend in with the world inhabitants by changing their physical appearance.
Because Kingdom Hearts was a collaboration between Disney and Squaresoft, it features a mixture of familiar Disney and Square characters, as well as several new characters created and designed by the director, Tetsuya Nomura. The primary protagonist of the game is Sora, who is chosen to wield the Keyblade, a sword-like weapon for battling darkness. The game also features two of his friends, Kairi and Riku. For most of the game, Sora is joined by Donald Duck and Goofy. Donald, the court wizard, and Goofy, captain of the royal guard, were sent from Disney Castle to find the Keyblade. The three join forces to search for King Mickey Mouse, Kairi, and Riku. The primary antagonist is Ansem, who is seeking to find power and knowledge by using dark beings called the Heartless. The Heartless, hearts corrupted by darkness, serve as most of the enemies encountered in the game and come in a variety of shapes and sizes.
As a game meant to explore the fictional universes of various Disney films, there are over 100 Disney characters. While many serve as major characters in the story, others appear in cameo roles, such as the One Hundred and One Dalmatians puppies playing a part in a side-quest. Most worlds also feature a Disney villain whom the player must defeat. The player can summon various Disney characters to fight alongside Sora in battle, causing Donald and Goofy to withdraw from the battlefield for the duration of the summon. Available summoned characters include the Genie from Aladdin, Tinkerbell from Peter Pan, Bambi from Bambi, and Simba from The Lion King.
Square also incorporated several characters from the Final Fantasy series into the game, though the characters were slightly altered to fit the game's back-story. On Destiny Islands, the player meets younger versions of Tidus, Wakka (both from Final Fantasy X), and Selphie Tilmitt (from Final Fantasy VIII). In Traverse Town, the player encounters Squall Leonhart (known in the game as "Leon") from Final Fantasy VIII as well as Aerith Gainsborough, Cid Highwind, and Yuffie Kisaragi from Final Fantasy VII. Rikku from Final Fantasy X and Irvine Kinneas from Final Fantasy VIII were both originally set to make cameo appearances, but were replaced by Yuffie and Wakka respectively. Cloud and Sephiroth (both from Final Fantasy VII) make appearances in Olympus Coliseum, where the player can fight them in tournaments. The emphasis on characters from later Final Fantasy installments stems from Nomura's hesitation to use characters he did not design.
The game also uses other Final Fantasy icons. Moogles appear to provide item synthesis. Several weapons, such as "Lionheart" and "Save the Queen", share names with other weapons from previous entries in the Final Fantasy series. A name Riku suggests for the raft early in the game is Highwind, a reference to the airship of Final Fantasy VII, while the default name for Sora's suggestion is Excalibur, a weapon in the Final Fantasy series. The magic-naming system in Kingdom Hearts (i.e. Fire, Fira, Firaga, etc.) is identical to Final Fantasy magic. The names of various spells are also the names of Gummi blocks, and various summons, weapons, bosses, and monsters are the names of Gummi ship blueprints.
Donald and Goofy use a Gummi Ship to travel to Traverse Town, to where Sora has drifted. Sora encounters the Heartless again, and meets Leon, who explains the Heartless are beings that consume hearts, and that the Keyblade is the only weapon capable of defeating them. A man named Ansem, the leader of Leon's home world, is said to have studied the Heartless. Sora meets Donald and Goofy and the three decide to travel together; Donald and Goofy to find 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 the Heartless use to take the heart of a world. A group of Disney villains, led by Maleficent, seek out the seven Princesses of Heart to unlock the Keyhole that leads to Kingdom Hearts, a repository of knowledge and power and the source of all hearts. This group includes Riku, whom Maleficent promises she will help in finding Kairi. Maleficent sows distrust in Riku, telling him Sora has 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, the homeworld of Ansem and the headquarters of Maleficent. Riku takes the Keyblade from Sora, revealing him as the true Keyblade master and that Sora only received it in his absence. Donald and Goofy, taking their order to follow the "key" seriously, leave with Riku. Sora challenges Riku, stating his heart derives strength from his friends; his friends return to him, as does the Keyblade. In his shame, Riku meets a cloaked man who goads him to give into the darkness. The three engage and kill Maleficent, but then meet a strangely-behaved Riku with a Keyblade that unlocks hearts. Sora finds Kairi's body and Riku, who reveals himself to be Ansem, possessing Riku's body. Ansem explains that Kairi is a Princess of Heart and her heart was trapped within Sora's body since Destiny Islands were destroyed. After defeating Ansem, Sora uses Ansem's Keyblade to unlock his heart by impaling himself, 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. Sora is restored to human form by Kairi and resolves to confront Ansem.
Ansem is found in End of the World, the combined remnants of worlds taken by the Heartless. Ansem explains his belief that the nature of the heart revolves around darkness, and he seeks Kingdom Hearts, as that would be the ultimate darkness. However, upon opening the door to Kingdom Hearts, 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, separating Sora and Kairi. The game concludes as Sora, Donald, and Goofy resolve to find Riku and Mickey.
Additional content was added to the North American release that was not included in the initial Japanese release: new optional bosses—one of which was named after the winner of the official website's "Name-In-Game" sweepstakes, an extra difficulty level, and a teaser of Kingdom Hearts II accessible by meeting certain criteria. Nomura included the teaser in hopes that fans would want a sequel. He was unsure if fans would want a sequel and felt that if they did not, then it would be best to leave certain events in the game unexplained. The new content was later added to the Japanese rerelease titled Kingdom Hearts Final Mix. Final Mix also included additional content such as new items, cut scenes, and enemies. The new content served as a canonical update to the original release and further hinted at plotlines that would be explained in sequels. Some content that did not make it into Kingdom Hearts was later added into Kingdom Hearts II. The "Pride Land" from The Lion King, for instance, was infeasible because a different program was required for Sora to be a lion and walk on four legs. Tifa Lockhart was considered to be included along with Sephiroth, but was left out due to time constraints.
Criticism about the gameplay was mixed. Many reviews complained that the camera was at times frustrating and the Gummi Ship portions were out of place. GameSpot cited "tedious" gameplay and Gummi Ship sections as "pale imitations of the Star Fox series", but stated that the combat was fun, particularly the boss fights. Dengeki Online commented on the camera controls, saying that the camera would often run into objects while being rotated by the player. GamePro compared the battle system to "old N64 Zelda games" and had positive comments about Donald and Goofy's artificial intelligence.
GameSpot commented that the concept of mixing the serious elements of Final Fantasy with the lighter elements of Disney seemed impossible, but was pulled off quite well. Because of that they awarded Kingdom Hearts "Best Crossover Since Capcom vs. SNK" in their 2002 Best and Worst of the Year awards. GameSpy cited that the periodic departure from the main plot into the Disney side stories was disappointing, and when the original plot builds to a climax, "...the story fails to gel thanks to a confusing mish-mash of vague terms and symbolism that probably made more sense in the director's head than in this final product." Aside from the plot, they stated the overall package was worth playing through to the end. G4TV awarded it "Best Story" at their 2003 G-Phoria awards show. Fan response was also positive; Kingdom Hearts was voted as the 19th best game of all-time by readers of the Japanese magazine Famitsu, 16th by the users of website GameFAQs, and 92nd by IGN users.
Released only in Japan, Kingdom Hearts Final Mix has 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 "Unknown", in an attempt to raise interest for the sequel.
In another attempt at foreshadowing, a video titled "Another Side, Another Story [deep dive]" plays at the ending if the player accomplishes certain tasks. New music tracks incorporated were "Disappeared" and "Another Side". The "Night on Bald Mountain" and "One-Winged Angel" tracks from the English version were included as well. Other changes include new abilities, new weapons, new items, additional and recolored enemies, and gameplay tweaks to make the game easier for the player, along with two new levels of difficulty. When first released, Final Mix included either a deck of Kingdom Hearts cards or special music CD. A limited "Platinum Edition" version of Kingdom Hearts Final Mix was later released with an action figure of Sora, a sticker set, and sketches of some of the main characters.
The manga series has had moderate success. The first volume was ranked 95th in USA Today's "Top 150 best sellers" during the week of its release. IGN praised Amano's artwork and commented on wanting to replay the game after reading. They criticized the lack of new content and stated the transition from game to print lost most of the story's appeal. The series was followed by a second manga series, Kingdom Hearts: Chain of Memories. Kingdom Hearts was also rereleased in three volumes in Japan in December 2006 as "Kingdom Hearts: Final Mix".