Death is a demon class tied to Mephisto Pheles, the King of Time. While not much is explicitly stated about Death demons as a whole, they're generally understood to be connected to Mephisto's domain and power structure. The exact nature of this relationship—whether Death demons serve under him, share similar abilities, or simply exist within the same supernatural hierarchy—remains somewhat vague in the series, but it's clear they're part of his sphere of influence.
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