Translation: giant priest
Alternate names: many variations and different kinds exist
Habitat: any; usually found in mountainous regions
Diet: varies; most commonly livestock or humans
Appearance: Ōnyūdō is a catch-all term for a number of giants found throughout Japan. The name is used in a euphemistic way; while some ōnyūdō bear a strong resemblance to Buddhist priests and monks, most have no actual relation to the clergy. Size, appearance, and mannerisms vary from region to region and account to account. Some giants are only slightly larger than a human while others are as big as a mountain. Some are saviors of men, while others are man-eaters.
Behavior: Ōnyūdō can be separated into four general groups: those that harm humans; those that help humans; transformations of other yōkai; and other, truly unique ōnyūdō that do not fit into any of these categories.
Ōnyūdō that harm humans are by far the broadest category. Among them are well-known yōkai, such as hitotsume nyūdō, mikoshi nyūdō, and the ocean going umi bōzu. These giants delight in terrorizing humans— sometimes hunting them to eat, sometimes pillaging and destroying villages out of rage, and other times terrifying lone travelers just for the fun of it.
Ōnyūdō that help humans are much rarer. They have been known to perform good deeds such as turning stuck waterwheels, moving heavy objects, or doing other things that require incredible amounts of strength. Though helpful, they are not always friendly. Ōnyūdō can change from benevolent to violent with little warning.
Helpful or harmful, true ōnyūdō are actually rare. Transformed yōkai—especially tanuki and itachi—make up a large percentage of the giant population. Shape-shifting yōkai take on giant form in order to scare people and cause mischief, though they rarely kill. There is no easy way to identify if a giant is a true ōnyūdō or just a shape-shifter. The two are functionally indistinguishable.
And then there are the remainder of the ōnyūdō—enigmatic and mysterious. They are only evidenced by their footprints or discarded trash. Regardless of how good or evil at heart a particular ōnyūdō is, they are by nature extremely dangerous. It is generally wise to leave them be. Better to avoid all contact with them than risk enraging an ōnyūdō and bringing destruction upon nearby villages.