Kingdom Hearts: Chain of Memories is a combination between a role-playing video game and collectible card game. The main role-playing aspect is an experience point system that is used to increase the character's maximum health or Card Points, or to learn a new skill. The cards are utilized in the progression of the story as well as in combat. The game features a field map and battle screen. The field map is an isometric area where the player can traverse between rooms. Enemies inhabit the field map and track the player to engage in combat, which can be initiated through contact between the player and an enemy. Once combat has been engaged, the game switches to the battle screen which utilizes a card-based battle system. A unique aspect to this game is "room synthesis": to advance through the game, the player must utilize Map cards that he has found after winning battles to synthesize rooms. The properties of each room―including quality of items and strength of enemies―are determined by the Map cards that the player chooses. Each card has a specific effect: red cards affect the number and type of enemies; green cards affect the power of the player's deck; and blue cards affect the properties of the room itself, such as allowing treasure chests or a save point to appear. The game features three modes of gameplay. The first two are story modes that feature either Sora or Riku, and the third is a two player battle mode. Initially only Sora's story mode is available; once completed, "Reverse/Rebirth" mode becomes available. Reverse/Rebirth allows the player to play a second story mode featuring Riku and a link mode where players can battle each other via a Game Link Cable. Combat uses a card-based battle system executed in real time. The player can jump and maneuver around the battle screen as they would on the field map, but all physical attacks, magic, items, and summonings are activated by playing cards. Cards are ranked from zero to nine, and are used for making attack combos or breaking enemy cards. With the exception of zero-ranked cards which are more expensive in terms of Card Points (CP) compared to other cards of the same type and have other ranks, more CP are required to place higher-ranked cards in the player's deck. Card Points—increased through level up—limit the number of cards the player can use in a deck. Cards with rank "zero" can break any opposing card or combo if played after the opposing card or combo, but they can be broken by any card or combo as well if it is played after the zero card is played. Breaking an opposing card will cancel that attack and stun the loser of a card break for a short time. Special enemy cards may be obtained by defeating enemies and bosses, and are used to give the player a temporary ability, ranging from enhanced offensive and defensive capabilities to modifying the attributes of certain cards. Combining cards in sets of three will create combo attacks that are usually more difficult to break because the rank of the combo will be the sum of the ranks of the three cards in the combo. Certain card combinations will create a "sleight", a special combination that will create a powerful physical attack, magical spell, or summon attack. When the player runs out of cards, the deck must be reloaded. Additionally, using a card combination will cause the first card in the combo to become unusable until the end of combat. Sora's and Riku's stories differ gameplay-wise in several ways. In Sora's story, Sora obtains cards by defeating enemies or through Moogle Shops. In some cases, Sora must earn the specific card first through a plot event before it becomes available. Sora can create and store three different decks in the pause menu. Unlike Sora, Riku has a closed deck that cannot be customized. The cards in his deck change depending on the world in which he is traveling. Riku is limited to mainly physical attacks, enemy cards, and Mickey Mouse ally cards. Riku can activate "dark mode" and unlock his sleight attacks if he accumulates enough "dark points". Dark points are earned by breaking enemy cards and combos, and the difference between Riku's card or combo and the enemy's card or combo is how many dark points he will accumulate for that card break.