The Fullmetal Alchemist.

A boy from another world possessed by a soul, the supreme leader of the vengeful spirits, an alchemist who masters both magic and martial arts, makes even the demon gods tremble before my puppet legion

A failed chemistry experiment caused the experimenter Gong Hao to soul-transcend into another world, becoming a common boy named Rui Glaire. Unfortunately, he was sold to Nightmare Island—the Empire's secret alchemical experiment base—where he served as the lowest-tier servant and was at risk of becoming experimental material at any moment. Fortunately, he still had a little time to change his fate: he desperately absorbed various knowledge and skills, learned and transformed the lost ancient alchemy, and aimed to become the most powerful and versatile alchemist proficient in both magic and martial arts.