The Kept Man of the Princess Knight, Vol. 1 (light novel)

In a corrupt dungeon city, a man and the woman who owns him live out their lives. Arwin, the Princess Knight, is like a spotless crimson flower among the filth of this place. Matthew, one of the local adventurers, is among the lowest of the low, as far as anyone knows. He's a weak fighter and a coward, and he spends his money on alcohol and gambling. But no one knows the truth–he serves his princess knight, and he'll get his hands as dirty as he has to for her sake.