Houfuku no Ansatsu Ningyou (Assassin Doll)

Ryot is a 62-year-old retired veteran. Once hailed as a legendary "Hero," he vanished at the end of the war to live out his twilight years in a remote village with his beloved grandchild. But Ryot holds a dangerous secret: he is a master artificer whose creations are forbidden "Mythic Items," capable of toppling entire nations. When greedy forces come after his creations, both Ryot and his grandchild are ruthlessly murdered. With his dying breath, Ryot activates a taboo skill, transferring his soul into his greatest masterpiece—the ultimate Assassin Doll, "Ray" and awakens in a flawless, youthful body. "Actions have consequences. Allow me to teach you what that means." Now, a merciless doll harboring the soul of a hardened veteran is about to drag everyone who wronged him straight down to hell!