in the first volume,the protagonist (jacob) gets hit by a car and reincarnates into another world.in his previous life,jacob was mentally disabled and spent his time alone at home.in his new life,he reincarnates as a young child in a family of peasants.he discovers he can use a rare type of magic only used by a legenday hero over 900 years ago during the raneth invasion,a species of insectile monsters with human-like intelligence that have carapaces stronger then tungsten,capable of using both magic and weapons as well as dragon mounts.