Sleepy Princess in the Demon Castle manga volume 26 features story and art by Kagiji Kumanomata.

Twilight, Zeus, and the princess must prepare to face a truly harrowing challenge - attending incognito at the Goodreste Royal Academy! However, things quickly go awry when they encounter a group of demon-obsessed students, a mysterious grimoire, and the most dangerous enemy they've ever faced. Then Demon Cleric deals with some non-Syalis feels, Odile's vacation fail ends with him getting eaten by a whale, a princess possessed by a father proves a bother, and more!