Mr.War -Saikyou no Moto Gunjin-

They called him Mr. War—a legendary soldier feared by enemies and allies alike. George, a master of battle and elite member of a special forces unit, met his tragic end through betrayal on the battlefield. But death wasn’t the end for him. He wakes up reincarnated as Michio, a slave laborer in a slum wasteland known as “Scrap Island,” where violence and exploitation rule the day. Stripped of rank, weapons, and identity—but not his ruthless survival instincts—Mr. War begins a new war. Armed only with his brain and brutal military training, he starts from the bottom of this hellish society and begins climbing his way to dominance. In a world where the strong prey on the weak, the battlefield has simply changed—and Mr. War never loses.