Strange rumors are circulating the Human Village.
"A dog with a human's face was rummaging the compost pile." "Somebody saw an old woman selling humans' feet."
These pointless rumors have exploded, and driven the children into fear. Unlike the youkai whose natural purpose is to attack humans, these rumors are both unsettling and impossible to discern the truths underneath. Since there were no real victims, the adults have come to think of them as merely children's silly talks.
Of course, the girls are not afraid. They know these to be the outside world's "urban legends" (made-up stories).
Urban legends have an interesting property. As the circulating rumors change, the anomalies will change correspondingly.
Reimu and company have assumed the rumors that fit them, and treat the anomalies as their playthings. As long as one can control the rumors without being afraid, the manifested anomalies can be rendered harmless. More than that, they can be turned into powers of one's own. The girls thought of controlling the urban legends by themselves as a necessary measure for keeping people from harm.
This had indeed been true. Until one night...