Su Mu lives in a war-torn age. His entire family has perished, leaving only his young granddaughter by his side. When the authorities forcibly conscript teenage boys into the army, the hundred-year-old man volunteers to enlist in her place to protect her, provoking ridicule from everyone. Just as battle approaches, he awakens the Hundred-Year-Old God of War System. On the battlefield, his marksmanship is peerless. Charging alone into enemy ranks on horseback, he strikes fear into tens of thousands of enemy soldiers, none of whom dares to confront him. After the war ends, the emperor personally summons him for an audience. Su Mu calmly declares that even at a hundred years old, he can still defend the nation's borders. From then on, he fights across the land, safeguarding his country and its people, and earns the title of the nation's revered God of War through his extraordinary military achievements.