Riku is a central character in the Kingdom Hearts series, which combines elements from Disney and Square Enix worlds. He starts as the best friend of the protagonist, Sora, but becomes one of the series' most complex characters as he struggles with his inner darkness. Riku's journey revolves around redemption and self-discovery, making him a compelling figure who often acts independently to protect his friends. He eventually becomes a Keyblade Master, showcasing his growth and determination to overcome his darker impulses.