The story takes place in Donorok, in the country of Noctum. After Noctum’s king Aster disappears, chaos rules the world. The relations between Monsters, Mongos and Dreamers are unstable, and Donorok – the country so heavily influenced by the chaos – slowly absorbs the land from the surrounding regions. Balder has taken over and has ordered the monsters to keep all children falling into Nightmare. The key to continuing his rule is Nightmare Boy, Billy.