Reincarnation into the Barrier Master

Story:

Opening his eyes, Kubota Tamotsu (34 years old) found himself in another world, and even in the body of a 6-year-old slave with the unusual skill "Level 1 Barrier". To transcend his limitations and become a powerful master of the "Barrier", Kubota is ready to do anything. But first, a hell of a workout full of obstacles and struggles.