All Coffin Princesses have a second pair of ears that pop up when they use their abilities. Other than those, they appear nearly identical to humans.
While individual personalities exist, all Coffin Princesses will seek to be loved by their master and protect them no matter what. If they fail to do so, there is a very high chance they will go on a rampage.
The Princesses first appeared on Hatsumi Island when a Voyager appeared and used their power to get rid of the Kanshu terrorizing the island. When the Voyager died, they went back to sleep in their Cocoons and they were entrusted to the Takao, Ootori, and an unknown family. Whenever the Kanshu returned, they would awaken a new princess and the cycle would repeat.
It was later revealed that the Voyager was the one who brought the Kanshu to the island in order to gain their trust and live a life of comfort from their gratitude.