今昔物語集
The "Konjaku Monogatarishū", a collection of stories published in the late Heian period, contains some of the earliest tales of "tengu", already characterized as they would be for centuries to come. These "tengu" are the troublesome opponents of Buddhism, who mislead the pious with false images of the Buddha, carry off monks and drop them in remote places, possess women in an attempt to seduce holy men, rob temples, and endow those who worship them with unholy power. They often disguise themselves as priests or nuns, but their true form seems to be that of a kite.