Arriving from the mysterious Otherworld, Nio spends her time in seclusion atop a sacred mountain that happens to be a tourist spot for humans of the Mundane world. As time passes, and her interaction with humans reach a new point, Nio descends to the human city below but forgets to hide her horns as she does so. No worries though as the human take her appearance as common cosplay. An act she mildly leans into as Nio spends more and more time engaging with the humans of this world. Especially as she enrolls in a human high school.