Sweet Dreams in the Demon Castle by Kagiji Kumanomata — Ongoing

Also known as Sleeping Princess and Maou-jou de Oyasumi

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The princess of the human kingdom has been kidnapped by the demon king!
But all she wants to do is get a good nights sleep!?

Chapter 1: The Princess in the Sleepless Castle released Jun 25 '16
Chapter 2: Bedsheets Shining Like the Sea released Jun 26 '16
Chapter 3: A Sweet Sleep Known as Death released Jul 25 '16
Chapter 4: Sleeping with the Wind Shield... and Nothing Else released Aug 16 '16
Chapter 5: Because There's a Tower There released Aug 17 '16
Chapter 6: Keep Howling at the Moon released Aug 18 '16
Chapter 7: The Dreaming Poison Mushroom released Aug 25 '16
Chapter 8: The Princess's Three-Star Armour released Sep 1 '16
Chapter 9: But, It's a Heavy Price to Pay, Isn't It? released Sep 9 '16
Chapter 10: Schlaf' ein holdes Kind released Sep 16 '16
Chapter 11: You Won't Go Down Unless You Touch It released Sep 23 '16
Chapter 12: The Sea of Pillows and the Tower of Babel released Oct 2 '16
Chapter 13: Head to the Sacred Treasure Forest! released Oct 10 '16
Chapter 14: The Steam Killing Demon released Oct 19 '16
Chapter 15: Innocent Villain released Oct 28 '16
Chapter 16: Princess Finisher-sama released Nov 9 '16
Chapter 17: She Looks Like the Princess and has the Same Brains as Her Too released Nov 18 '16
Chapter 18: Friend (Futon) released Nov 25 '16
Chapter 19: Badump! The Training Tournament Filled With Demons released Dec 4 '16
Chapter 20: A Flower's Life is Short released Dec 19 '16
Chapter 21: Why Can't Honey Be Produced From Nothing released Dec 26 '16
Chapter 22: Guardian of the Quiet Sleep released Jan 3 '17
Chapter 23: I'm Going to Visit You Tonight released Jan 17 '17
Chapter 24 released Feb 1 '17
Chapter 25: On a Cradle Unto the Grave released Feb 20 '17
Chapter 26: Demon King Castle (Sleep) Paralysis Play released Mar 1 '17
Chapter 27: The Sloth Making Machine released Mar 15 '17