Sleepy Princess in the Demon Castle manga volume 29 features story and art by Kagiji Kumanomata.

The Plenary Demon Conference is finally here! With all the Demon World's movers and shakers gathered in one spot, surely there's no way whatsoever that Princess Syalis will mess it up - certainly not by becoming a giant nightmare-infused monster bearing the dark and hidden secret behind the origin of the ongoing war between the humans and the demons! Also, there's some good ol' fashioned dungeon crawling!