Searching for a Book with a certain setting.

[Thomus]

I just recently finished playing Dishonored, and the character relationship intrigued me.

It's a ruler/bodyguard type of fiasco. I really enjoyed the concept, but it was not exactly flushed out being a game and I haven't a book I am currently reading so am hoping to find one with that similar sort of situation.

Someone being devoted entirely to the protection of another, and how that can be. In a Fantasy/Sci-Fi/Historical setting. One that centres on the development of such close characters whilst still having a plot. (I know awfully specific, but one can hope!)

Unfortunately, I have no idea how to begin searching for such a specific sort
of book.

If anyone can point me in the right direction or offer some suggestions I would appreciate it! I