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Satan; the Devil; the Prince of Darkness
king of the demons who try to prevent people from doing good
勇者はついに魔王を倒した。
The hero finally defeated the Demon King.
暗い森の奥から、魔王の低い笑い声が響いてきた。
From deep in the dark forest, the Demon King's low laughter echoed out.
魔王の城は難攻不落で、誰も近づけなかった。
The Demon King's castle was impregnable, and no one could approach it.