Sleepy Princess in the Demon Castle Vol. 13 (manga)
The Demon King and his troops travel to a demilitarized zone bordering the demon world and the human world for some intense physical training alongside their human counterparts. When one group mocks the other, Syalis is hell-bent on putting them in their place! While the Demon Castle recovers from boot camp, the princess saves the day...and wrecks it even more. Then, an integral member of the Demon Castle staff resigns and heads for home...with the rest of the demons and one human in hot pursuit!