Sleepy Princess in the Demon Castle, also known as Maou-jou de Oyasumi, is a funny fantasy manga about Princess Syalis. The Demon King captures her and takes her to his castle. However, Syalis does not worry about her fate. Instead, she only wants to get a good night’s sleep. Soon, she learns that the castle has poor beds and uncomfortable pillows. Therefore, she starts looking for better ways to sleep. She explores the castle and takes anything that can help her rest. As a result, her simple goal causes trouble for the Demon King and his demons. Along the way, Syalis meets many strange and funny monsters. She also turns the demon castle into her own place to relax. Meanwhile, the demons try to stop her many plans. Each attempt leads to a new and funny adventure. With cute characters, simple comedy, and a fun fantasy world, Sleepy Princess in the Demon Castle offers an enjoyable story for fans of comedy, fantasy, and slice-of-life manga.