Young man bonds with a slave, he is a mage and royalty. His father is also a mage and a complete dick. Mages in this world draws power from their bonded slaves. There is drama and intrigue as he tries to hide/ keep the girl and figure out her mysterious past.
I know the story you are looking for but not the tittle or the autor. He pulled the stories here years ago.
Could it be Tales of Tanitsar by Argon. Don't know if mages are involved but the mc is a prince who gets a new slave and with her help ends slavery and takes over other nations.
https://storiesonline.net/s/72279/the-tales-of-tanitsar
