Kekkaishi e no Tensei

Kekkaishi e no Tensei (結界師への転生, lit. "Transmigration of Kekkaishi")(Reincarnation into the Barrier Master) is a light novel series by Naotarou Kataoka with illustrations by Itsuwa Katou.

Plot
When he opened his eyes, Kubo Tamotsu (34 years old) was reincarnated into the different world. He was reincarnated as a 6 years old boy with a「Barrier Lv1」skill. But his status was a 「Slave」. In order to escape from his harsh circumstances, achieve「Peaceful life」, and be「Surrounded by beauties」, those were his dreams from the previous life, he decided to struggle with all his strength.

Other Sources
* https://www.novelupdates.com/series/reincarnation-into-the-barrier-master/

* http://isekaiscan.com/manga/kekkaishi-e-no-tensei/