Kingdom Hearts: Chain of Memories
Released in December 2004, Kingdom Hearts: Chain of Memories follows Sora and friends as they explore Castle Oblivion well before the events of Kingdom Hearts 2. The game features a new battle system, where you can organize cards of different numerical values and types to form all sorts of different spells and attacks. This is the only Kingdom Hearts game where you get to play as Riku, and the first to feature a multiplayer mode. Alas, people complained about the card system, so Tetsuya Nomura redefined the battle style for Kingdom Hearts 2 so that you could defeat almost every enemy simply by pressing the Triangle button.