A brief description of the manga The Slave of the “Black Knights” is Recruited by the “White Adventurer’s Guild” as a S Rank Adventurer:
I was a slave in a knightly order, where I suffered humiliation from my elders, but I was found by a beautiful little girl who called herself a guild master.
At first I didn’t take everything seriously, but after being offered a huge amount of money, I decided to leave the knightly order. When I came to the guild, I was even given the S-rank title.
This is the success story of a man who has had nothing since birth.