The story follows Princess Syalis, a young princess who was kidnapped by the Demon King, and her quest to sleep well while imprisoned.

An anime television series adaptation produced by Doga Kobo aired from October to December 2020. It has been serialized in Shogakukan's Weekly Shōnen Sunday magazine since May 2016, with its chapters collected in twenty-five tankōbon volumes as of July 2023. 'Good Night in Demon Castle') is a Japanese manga series written and illustrated by Kagiji Kumanomata. Sleepy Princess in the Demon Castle ( Japanese: 魔王城でおやすみ, Hepburn: Maōjō de Oyasumi, lit.