I Transmigrated to Another World and Leveled Up to 999

Sangji, a modern-day construction worker, transmigrated into the body of a five-year-old boy in another world. He survived on pig slop and stolen dog food until, at twelve, he activated an Infinite Upgrade System. He stockpiled weapons, trained spirit pets, and embarked on a path of slaying monsters, leveling up, and defying fate to cultivate immortality.