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Riku  is Sora's and Kairi's best friend, and character created by Tetsuya Nomura for the Kingdom Hearts series.Nomura has stated that Riku's name can be interpreted as "land"; the Japanese on'yomi pronunciation of land is riku .  He is playable in the second story mode of Kingdom Hearts: Chain of Memories and as a world-specific ally in Kingdom Hearts II. In 358/2 Days, Riku is playable in the multiplayer mode and also serves as the final boss in the game's story mode.

Source from Wikipeida