Ayakashi (妖) is a collective name for yōkai that appear above the surface of a piece of water.
In Nagasaki Prefecture, kaika that appear above the surface of water are so called, and the funayūrei of Yamaguchi and Saga Prefectures also have the same name.
In the western part of Japan, they are supposed to be those who died at sea and try to lure people to join them.
In Tsushima, they are also called kaika of ayakashi (ayakashi no kaika) and appear on the beaches in the evening and it seems that a child walks in the middle of the fire.
On the coasts, kaika seem to be mountains and obstruct the path of the traveler and have the reputation of disappearing if one does not avoid the mountain and tries to hit it hard.
A folk belief claims that if a tapered remora, a real fish, gets stuck in the bottom of the boat, it is not able to move, so ayakashi is a synonym for this kind of fish.
In Toriyama Sekien's Konjaku Hyakki Shūi, the ayakashi is represented by a large sea serpent, but it may be an ikuchi.
In the Kaidanoi no Tsue, a collection of ghost stories from the Edo period, they are as shown below. It is in Taidōzaki, in the Chōsei district of Chiba prefecture. A certain ship needs water and comes ashore.
A beautiful woman brings up water from a well and thus retrieves the water needed by the ship she is joining. When this is reported to the boatman, he says, "There is no well in this place.
Long ago, someone who needed water came up to this land in the same way and disappeared. That woman was the ayakashi.
When the boatman hurriedly launched the ship, the woman ran and bit into the hull of the ship. Without delay, they force her away by hitting her with the oar and manage to escape.