Kemurikage

"Supposedly, when children misbehave, the Kemurikage come and snatch them away in the middle of the night."

- Mai explaining the legend of the Kemurikage The Kemurikage spirits from Fire Nation legends, and one of the primary antagonists of the Smoke and Shadow comic trilogy, the fourth trilogy to take place between Avatar: The Last Airbender and The Legend of Korra.

The Legends
Parents from Mai's home village would often tell their children that when they misbehaved, spirits from the mountains called the Kemurikage would snatch them away in the middle of the night. Michi heard the stories as a child and told them to her children as well.

New Ozai Society
On the eve of Yu Dao's inaugural celebration, the Kemurikage appear before Ukano and berate him for his failures as governor of New Ozai. They offer him a chance at redemption by telling him to overthrow Zuko and reinstate Fire Lord Ozai, arguing that stability and safety come from strength. After failing the first time, the Kemurikage offer him a second chance, giving him a month to make good on his mission, else they take away all he holds dear.

One month later, when Ukano has still not yet disposed of Zuko, the Kemurikage raid Mura's flower shop and kidnap Ukano's son and Mai's brother, Tom-Tom. Mai demanded to know who they are and what they wanted, but the Kemurikage simply disappeared stating they already had what they wanted.