Sleepy Princess in the Demon Castle

Sleepy Princess in the Demon Castle (魔王城でおやすみ, Maou-jou de Oyasumi) is a shonen manga by Kagiji Kumanomata. It began its serialization in the Weekly Shonen Sunday magazine in May 2016. Viz Media has licensed it for release in English.

Plot
After a princess is kidnapped by demons, she decides to while away the hours by sleeping, but getting a good night’s rest turns out to be a lot of work! She begins by fashioning a DIY pillow out of the fur of her Teddy Demon guards and an “air mattress” from the magical Shield of the Wind. The princess’s hapless demonic guards soon discover that their captive expects to be treated like, well, a princess. Things go from bad to worse—for her captors—when some of Princess Syalis’s schemes end in her untimely—if temporary—demise and she chooses the Forbidden Grimoire for her bedtime reading…

Official
Official English site