One day, Kubo Tamotsu, an ordinary office worker, is suddenly reincarnated in another world as a 6-year-old slave. Picked up by the Basam Marquess, he was raised as "Linus," a Barrier Master, and continued developing his abilities at a remarkable rate. Just when he was on the verge of serving as a Royal Barrier Master, the Palace comes under attack by foes unknown. Linus heads to help his Masters, but--?!