Ningyo.

Ningyo (人魚, にんぎょ) is not originally the graceful Western mermaid most modern readers expect. In older Japanese sources it is often more fish than human, a strange body with a human-like face, human-like upper features, or occasional limbs set onto a scaled aquatic form. Some descriptions make it small and pitiable, others uncanny and malformed, and many stress its sheer wrongness rather than beauty.

That older visual instability is one of the creature's defining features. Only in the Edo period, when encyclopedias, popular fiction, rangaku knowledge, and printed broadsides spread more widely, did ningyo begin to overlap strongly with the familiar half-human mermaid image. Even then, the Japanese creature often kept an ominous, animal, or grotesque quality absent from romantic European mermaid lore.

Ningyo is usually encountered as a sign, not a companion. Strange catches and strandings are read as omens of war, disorder, or coming disaster in medieval and early modern records. At the same time, another strand of tradition treats its flesh as a source of impossible longevity. That tension, dread on one side and miraculous life on the other, makes ningyo one of the most ambivalent beings in Japanese folklore.

People therefore approach it badly and at their peril. Fishermen may net one by accident, rulers may receive one as a prodigy, and curious households may try to turn it into food or medicine. Yet the creature resists ordinary handling. Even when it becomes an object of appetite, curiosity, or display, the stories insist that the human world has touched something it does not fully understand.