Kenkoku no Jungfrau

In ancient times, numerous kingdoms and faiths coexisted and clashed in a world without order. A demon emerged, impervious to weapons, magic, or knowledge. A sage declared the existence of a blade capable of slaying the demon and sought skilled warriors. Twelve kings each sent their most capable knight. The sage and the twelve knights fought the demon and succeeded in defeating it. The sage was then crowned king, uniting the twelve kingdoms. The knights became known as the Knights of the Round Table and set the standard for knighthood. This is the foundation of the present era.