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 Neverland 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.