Kekkaishi e no Tensei

At 34 years old, Kubo Tamotsu works at an exploitative company only to wake up one day in an unfamiliar world, reincarnated into the body of a six-year-old. Not aware of his innate “Barrier Master” skills, he finds himself on the slave market, and up for auction! When no one bids on him and he’s queued for disposal, he is rescued in the nick of time by Marquess Basam. He will be raised as the Marquess’ personal Barrier Master under a new name, “Linus,” and his talent as a Barrier Master will grow day by day. His troubles never seem to end, as he struggles to survive!

(Source: Seven Seas Entertainment)