Umi nyōbō are dangerous yōkai who live in the ocean. They resemble human women, but have many piscine features. Their skin is scaley like a fish, and their fingers and toes are webbed like a waterfowl’s and resemble fins. Their teeth are sharp and brilliant, like a shark’s. They are very strong, and very dangerous.
Umi nyōbō spend most of their time in the oceans. However, they are able to survive on land for several days without returning to sea. According to an entry for umi nyōbō in the Yamato honzō, a biology encyclopedia written in 1709, they are unable to speak. However, many folk tales depict umi nyōbō who are able to speak.
Folk tales from fishing villages describe umi nyōbō as fearsome predators who kill and eat humans for pleasure. However, this is not always the case. While they do prey on humans, it appears that they do have a sense of compassion as well, and can occasionally show kindness towards humans.
Umi nyōbō originates in the Izumo region of Shimane Prefecture, however similar stories are found along the Sanriku Coast and other coastal regions around Japan. These stories resemble those of other coastal yōkai which haunt fishing villages, such as iso onna. The Yamato honzō‘s umi nyōbō most likely refers to a ningyo, or mermaid, instead of this yōkai.
Umi nyōbō are often thought to be the reincarnated spirits of women who drowned in the sea. They are also sometimes said to be the wives of umi bōzu.
In Iwate Prefecture, two fishermen went out to sea and did not return. Their wives waited and waited for them, and began to worry. An umi nyōbō came upon the bodies of the two drowned fishermen in the sea. She disguised herself as a human and visited the fishermen’s wives. She handed them a package and left. When the wives opened the packages, inside were the severed heads of their drowned husbands. The women screamed in horror, and were so overcome with grief that they threw themselves into the sea and drowned. It is said that afterwards they became umi nyōbō themselves.
The best known umi nyōbō story comes from the village of Uppurui in Shimane Prefecture. An old man was asked by a friend to house sit while he was away. The old man had done this many times, and was used to it. However, while half-dozing, the man suddenly felt the strange sensation that he was being watched. He awoke and looked towards the window, where for a brief moment he caught a glimpse of a pair of strange and unsettling eyes watching him. The eyes quickly vanished into the night after that. The old man felt suddenly overcome with fear. He hid himself in the closet and held his breath.
A moment later, the old man heard somebody enter the house. He slid the closet door open a crack and peeked into the room. He saw a woman with long hair—only, her body was covered in scales, and she had webbed hands and feet! He realized that the creature who had been watching him was an umi nyōbō.
The umi nyōbō was carrying a red-faced newborn human baby in one arm. The old man watched as she entered the kitchen and began to snoop around. She approached a barrel of pickled fish which had a heavy stone placed on top of it to keep the lid sealed. While still carrying the human baby, she effortlessly lifted and tossed away the stone with one hand. She grabbed webbed handful after webbed handful of picked fish and gleefully swallowed them whole. Her sharp teeth glimmered. When she had eaten all of the fish, she bit into the human baby and quickly devoured that too.
The old man was paralyzed with fear, and could not look away.
The umi nyōbō finished up all the remaining bits of pickled fish and human baby, then began to scan the house with her fierce eyes. “Where is that old man I saw in here earlier? I really could use something to clean my palate!”
The umi nyōbō scanned the house once more, but saw no sign of the old man. Disappointed, she left the house and vanished into the night.