Queen’s Knight Kael

Queen’s Knight Kael summary:

A 500-year-old, low-ranking demon knight Kael suddenly finds himself inside a royal secret chamber, summoned out of the blue by Yulia D. Beatrice Scachiel— the precocious queen of Nesland who only turned eight recently. As it turns out, she’s in grave danger of getting killed by mysterious monsters that have appeared out of nowhere, and Kael is her only way out of the castle to safety!