Sleepy Princess in the Demon Castle

Story

Sshhh! Princess Syalis is trying to get a good night's sleep. Some shut-eye. Forty winks. Catch some Z's. Long ago in olden times when people and demons lived together in—well, disharmony, really – a demon king kidnaps a human princess and imprisons her in his castle. Bereft, the princess's subjects beat their chests in anguish…until a hero arises to spearhead Project Rescue Our Princess! While waiting for her knight in shining armor, what's an imprisoned princess to do …? Teddy-bear guards with bat wings are all very well, but her dungeon cell is bo-o-o-ring!

Synopsis via AniList (English).