Hi this manga is about a young king or prince, the story opens with him killing this massive legendary monster (I can't remember if it's a dragon or not). He then was laying down and about to die, can't remember why ( i think he was born with a weak body) but he casts a magic that reincarnates him into a family of warriors who he finds out are ?servants, slaves? but they have extremely strong bodies. He grows up with a brother, and then later leaves the tribe to be a guard for some princess? Also, he hears that his previous self (the prince/king) is said to still be alive, and he's trying to find clues to see if that's true or not. Or if something inhabited his previous body.
Ars, the prince of the Kingdom of Karitz, who was called the strongest wizard, died at a young age. But on the verge of death, he uses reincarnation magic. Reincarnated as Wals Sai, a slave with the best body! Wals, who became the escort of a princess in a small country, became a matchless slave who used her best body and magic to crush all enemies! From "Become a Novelist"! A fantasy adventure by "the strongest slave", opening !! * "Become a novelist" is a registered trademark of Hina Project Co., Ltd.