Furuki Okite no Mahou Kishi

A knight named Sir Sid, known for his unmatched strength and magical abilities, served King Arthur in ancient times but was infamous for his dishonorable actions. According to legend, he was killed by the king himself. A thousand years later, a prince named Alvin, who is descended from Arthur and aware of the truth about Sid, summons him from the dead. Sid agrees to fulfill his old promise and helps Alvin protect the kingdom from an approaching threat. He also becomes a mentor to Alvin's group of trainee knights. As threats emerge, Sid teaches them to depend on more than just their enchanted swords, guiding them in the traditional methods of magic knights.