Is there a Monk or Fighter subclass similar to the Black Butler character?

The Black Butler anime series centers around a bodyguard / butler with, shall we say, a demonic flair. I would love to play a similar class in our upcoming Avernus campaign (say a subclass of fighter or monk, or maybe even a hybrid). I’ve found a couple of homebrew options, such as this Way of the Demon Fist monk subclass.

However, I was wondering if there is a subclass in the official source materials that matches what I’m looking. Homebrew is okay (though not preferred) – so if there are well-used homebrew options that you know of, that would be useful as well.

Relevant abilities:

  • Unarmed strike capabilities (a la monks)
  • Perhaps some sort of eldritch or hellfire-type magic ability