あやかし（あやかし）
Ayakashi
A sailors' word for a strange thing met at sea; now a loose word for spirits in general.
Ayakashi is what boatmen in western Japan called an apparition on the water: a light, a shape, a thing that clung to the hull. Toriyama Sekien drew an ayakashi in 1779 as an enormous sea serpent that takes days to pass over a boat, oozing oil the crew must bail. The word has no settled creature behind it, which is its point: it covers whatever the sea produced on a given night, from the drowned sailors of the funayūrei to the huge dark head of the umi-bōzu.
In anime and games of the last twenty years ayakashi has become a general word for spirits and yokai, sometimes used in preference to yōkai because it sounds older and stranger. In the records it stays at sea.
Related yokai
Funayūrei
船幽霊（ふなゆうれい）
A ruined boat draws alongside at night and its crew asks for a scoop. Give them an ordinary one, and they may use it to fill your boat with seawater.
Umi-bōzu
海坊主（うみぼうず）
One account describes a vast Buddha-like shape crossing ahead of a boat on a clear, windless day, then slowly thinning until it vanished.
Isonade
磯撫で（いそなで）
In the 1841 Ehon Hyaku Monogatari a shark-like creature of the western sea attacks with its tail — and in Kumano in 1960 the name was still the thing people said when someone died at the shore.
Iso-onna
磯女（いそおんな）
A 1929 record from Mizuho in Nagasaki describes a wrestler who tried to speak to a black-haired woman sitting on a shore stone at night — and other accounts from the same coastline describe something else entirely under the same name.