Kekkaishi e no Tensei

By the time he opened his eyes, Kubota Tamotsu (34 years old) has been reincarnated into another world. Moreover, as a 6 years old slave with "Level 1 Barrier" skill. To surpass his limitations and become a powerful Barrier master Kubota begins a hellish training, full of obstacles and struggles.
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[Original Web Novel](https://ncode.syosetu.com/n3631do/)
[Light Novel](https://bookwalker.jp/series/130407/)