The Boy Raised by the Demon Queen and the Dragon Queen Has No Rival

A boy named Ruisha is trapped in a distorted space created by the ancient hero. What he finds there is the Demon King and the Dragon King, who should have been defeated by the hero 300 years ago. Ruisha befriends the Demon King and the Dragon King, and is trained by them, going from a weak child to a legendary warrior with the power of both demons and dragons.