Battle cards (バトルカード, Batoru kādo?) are the primary mechanic for fighting enemies in Kingdom Hearts Chain of Memories. They replace most of the abilities and skills from Kingdom Hearts, including weapon skills, magic, summons, items and passive abilities.
Upon entering Castle Oblivion, Sora, Donald, and Goofy are confronted by Marluxia, who reveals to them that they have forgotten every ability they knew. After Sora enters the first floor of the castle with the Traverse Town world card, he faces Marluxia again, who introduces Sora to battling with cards.
Later on, the group encounters the memory-based version of Leon, who teaches Sora about card values, card breaks, and stocking cards.
When Sora or Riku enters a battle, they gain the use of the cards in their equipped deck. Pressing in Chain of Memories, or and in the English and Japanese releases of Re:Chain of Memories, respectively, plays the currently selected card from the deck, immediately activating its effect. The cards in the deck can be cycled by pressing the left and right shoulder buttons.
Cards that have been played become temporarily unavailable, until the Reload Card (リロードカード, Rirōdo kādo?) is used. Sora must charge the reload card in order to restore his cards to the deck to be played again. Each time the deck is reloaded, the reload card must be charged an additional time, up to a maximum of three times, although certain item cards can reset the reload counter to 1. Sora cannot charge the reload card while moving, except when the Reload Kinesis ability is in effect. Riku does not have to charge his reload card; it activates immediately. The reload card is not a card that needs to be added to a deck, but in Re:Chain of Memories, Sora can lose his reload card while battling Marluxia's third form.
Each battle card is marked with a card value between 0 and 9. A card break (カードブレイク, kādo bureiku?) occurs when a card is played at the same time as an opposing card with a lower value. The card with the lower value will be broken, halting the corresponding attack and causing the user to recoil, leaving them vulnerable to attack. Attempting to play a lower-valued card will result in failing to break the enemy's attack and wasting the card, while playing a card with the same value cancels both cards. Cards with a value of 0 can be broken by any card, but they can also be used to break any card or sleight, regardless of value.
Sora and Riku can stock up to three cards before playing them, by pressing the shoulder buttons simultaneously in the original release, or by pressing in Re:Chain of Memories. Stocked cards appear next to the HP gauge at the top-left of the screen, along with their combined card values. Stocked cards can be played in the original release by pressing the shoulder buttons simultaneously with three stocked cards, and in Re:Chain of Memories by pressing with three stocked cards, or pressing and simultaneously to one to three stocked cards. In the enhanced remake, stocked cards can be canceled with . When using stocked cards, the first card selected will be removed from the deck for the remainder of the battle, unless restored using certain Item cards or protected using Sleight Lock.
Playing stocked cards makes it difficult for attacks to be broken, and makes breaking enemy attacks easier. Additionally, certain combinations of stocked cards activate sleights, or special abilities, when played. Sleights become available for use under certain conditions, such as upon leveling up or obtaining a certain card. Many of Riku's sleights also require that he activate Duel or Dark Mode.
Human and humanoid enemies, such as the members of Organization XIII, can also stock cards and utilize sleights.
In Re:Chain of Memories, Riku can activate a Card Duel by playing a card with the same value as an enemy's card and pressing , or by using Duel Trigger. In a Card Duel, Riku must match or break a certain number of cards played by the enemy within a time limit. The number of cards and time limit depend on the enemy. If Riku succeeds, he executes a duel sleight, but if he fails, he becomes stunned.
Sora and Riku's decks determine the cards they can wield in battle.
Sora can alter the makeup of his deck, by adding, removing, or changing the order of cards. The deck cannot contain more than 99 cards, and it is further limited by Sora's maximum CP, or Card Points. Each card costs CP to be added to the deck, with more powerful cards and higher card values requiring more. Premium cards cost much less than standard cards, but if used in normal attacks, they cannot be reloaded in battle unless restored by certain item cards or protected using Premium Guard. Maximum CP can be increased upon leveling up. Sora can save three different decks that he can equip, each of which can be accessed from the Main Menu. Cards may be shared between decks.
Riku's deck is predetermined by the world and floor he is currently exploring and cannot be altered.
There are six types of cards that can be played in battle. Attack cards (アタックカード, Atakku kādo?) are colored bright red and represent weapon attacks. Playing them in succession creates a combo attack. Magic cards (マジックカード, Majikku kādo?) are colored bright blue and represent magic skills. Summon cards (召喚カード, Shōkan kādo?) are a subset of magic cards that temporarily call summons to the field in Sora's place. Item cards (アイテムカード, Aitemu kādo?) are colored bright green and are one-use cards that restore attack and magic cards to the deck. Friend cards are the same green color as item cards, and they summon one of Sora's party members to the field to fight alongside him. Unlike the other types of battle cards, friend cards are one-use cards that appear randomly during battle and are not retained after the battle ends. Enemy cards (エネミーカード, Enemī kādo?) are colored black and activate a passive ability, which lasts a set amount of time before it expires. Only one Enemy card effect can be in use at a time.
Gimmick cards appear randomly during Boss Battles. These cards are colored green, like item and friend cards, and have the Mickey Mouse insignia on their faces. When used, a special, temporary condition will appear on the field that assists Sora or Riku in attacking the enemy. For example, playing a gimmick card against the Parasite Cage will clear the acid from the field, making it easier to approach the boss.