As the name suggests, it is an octopus monster. Its appearance is the same as the ordinary octopus. However, when fishermen move their ship closer to capture it, it spreads the body as big as six tatami mats and tries to wrap the entire ship.
It is said that it usually stays inside of a shell and drifts in the sea.
In addition, the blanket octopus which is a real creature drifting in the ocean is commonly called "koromodako" by fishermen, because it has a thin membrane like a cloth between its legs. Moreover, species of paper nautilus which is similar to the blanket octopus are also drifting in the ocean, and the female of which secretes shells from its arms and wraps itself in the shell and incubates eggs in it.