Sleepy Princess in the Demon Castle, Vol. 2 by Kagiji Kumanomata

[Viz] A captured princess just wants a good night’s sleep! Shhh… Kidnapped by the Demon King and imprisoned in his castle, Princess Syalis is…bored. While waiting to be rescued, Princess Syalis makes herself at home by commandeering a bathtub, befriending (sort of) a cute demon girl and participating in a castle fitness challenge. Her plots to get some shut-eye include stealing ice from Ice Demons to cool off on a hot summer night, attempting to make her own waterbed, toying with magic spells and provoking an enchanted flower into releasing a soporific. And then the nightmares begin…