 Kingdom Hearts : Chain of Memories is the second game in the Kingdom Hearts series . It is a direct sequel to Kingdom Hearts , and its ending is set about a year before Kingdom Hearts II . The story centers on the protagonist of the first game , Sora , exploring a mysterious castle in search of his friends . As he ascends the castle , his friend and rival , Riku , explores the basement levels and fights his inner darkness . The game introduces new characters and plotlines that further expand the Kingdom Hearts universe and set up the premise for Kingdom Hearts II . 
