RYUK - $R is being protected by @SafeguardRobot

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Ryuk (リューク, Ryūku) is a Shinigami who indirectly gives Light Yagami a Death Note after becoming bored with the Shinigami Realm.

Ryuk doesn't even regards Light as friend. He just sees him as an amusement and a source of Apples. Yep. Ryuk can read Light lifespan, can kill Light and perfectly able to do so without remorse