The Avenging Assassin Doll Manga

Ryot, a 62-year-old retired veteran once celebrated as a legendary hero, lives quietly in a remote village with his beloved grandchild. He is also a master artificer whose forbidden Mythic Items are powerful enough to bring entire nations down. When greedy forces come after his creations, Ryot and his grandchild are murdered. With his dying breath, he uses a taboo skill to transfer his soul into Ray, his greatest masterpiece: an ultimate Assassin Doll with a flawless, youthful body. Carrying the soul of a hardened veteran, Ray sets out to make those who wronged him face the consequences of their actions.