Giant open-sea monster fish that can sink ships
Ayakashi
Ikuchi
The boatman sets down the oar and bails oil with a hat. For two days, then three, no one sees where the head begins or the tail ends.
Overview
Ayakashi is a giant eel-like sea yokai, also called ikuchi. Though not especially thick, it is said to stretch for thousands of meters and take two or three days to pass over a boat, spilling oil that must be bailed out or the vessel will sink.
Encounter
It appears at night in the open seas, especially off Hitachi. While the long body crosses a ship, sailors must scoop the accumulating oil with hats and throw it back into the sea.
Lore
Tsumura Soan's Tankai records a strange fish off Hitachi, and Negishi Yasumori's Mimibukuro tells of ikuchi in western and southern seas. Sekien's Ayakashi in Konjaku Hyakki Shui is thought to draw on this monster.
Traits
Its body is unimaginably long and secretes sticky oil as it passes. It does not directly attack people; the danger lies in the passive threat of drowning the boat beneath its oil.
It caught on the bow and writhed there for two or three days.
Mimibukuro