Amemasu

The sources do not provide a single origin myth for amemasu. Instead, stories locate very large amemasu in particular deep lakes (notably Lake Mashū and Lake Shikotsu in Hokkaidō) and relate episodic tales in which an amemasu's death or movements produce local landforms or hazards (for example, a corpse blocking a lake and later producing the Konsengen'ya plain when removed). Some accounts frame the largest amemasu as creatures that support the earth; when such a fish grows tired it may cause earthquakes, a role compared in the sources to the Namazu.

Described as giant fish- or whale-like lake creatures. Individual tales supply striking features (e.g., a head likened to a rock, an immense tail extending toward a river, or a belly torn open by a deer's antlers after being swallowed). Amemasu can also take human form, typically that of a beautiful woman; in that guise their skin is said to be cold and clammy, like fish skin, a diagnostic trait recorded in the sources.

Documented behaviors and powers include capsizing boats, drowning or killing humans who encounter them on lakes, and producing large-scale environmental effects such as blocking lakes with their carcasses and thereby threatening downstream flooding. In at least one regional legend an amemasu killed a hawk. Cosmologically, very large amemasu are described as holding up the earth and, when fatigued, causing earthquakes — a role explicitly compared in the sources to the Namazu. Some stories also depict amemasu using human disguise (usually a woman) to lure victims.