The story from the PS2 game is extending on the Game Boy Advance with this RPG collaboration between Square-Enix, Disney, and GBA developer Jupiter. Sora, the Kingdom Hearts' hero from the first game, wanders into a castle where he and his companions, Donald and Goofy, realize their magic and skills, earned in the first game, have been completely stripped away. Sora must traverse the castle on his own this time. Donald and Goofy must stay behind, but they'll accommodate Sora during battles as special attack "cards." When Sora encounters a dark force, players are booted to a battle arena where he must wipe out the threat using his keyblade and special skills. The game's exploration portions take place in an isometric perspective, and require a bit of platform-style skill of jumping and climbing up ledges. It's up to players to battle enemies to collect cards that will unlock doors to the next part of the map.
Using the special cards is key to traveling and advancing in Kingdom Hearts: Chain of Memories. The cards can be combined for a number of different spells, abilities, tactics and combination attacks. Doors can be unlocked and treasures can be discovered with the right cards. The keyblade can be used in striking objects to open them or in initiating an attack with an enemy. The enemies are called the Heartless and wander about each room. Avoidance is always an option but in confrontation, the first attack gives the player an advantage. The cards in the player's deck regulate each enemy confrontation, which are placed at the bottom left of the screen. Different cards can be used for magic spells, battle attacks, items, and summoning characters. Cards can be play singly or in groups for a combination attack. The enemies also use cards in battle so matching cards with adversaries can help with defeat. Card supplies can be depleted and only replenished by reshuffling the deck to start over. The more the deck is shuffled, the longer it takes to do so and can delay the ability to attack. Players must be careful, as shuffling will also leave them vulnerable to attack.