Koromodako

As the name indicates, koromo-dako is an octopus-like yōkai that appear small at first, but expands widely like a piece of clothing when a boat arrives, and sinks both vessel and humans in the sea.^[2][3]

The small octopus can expand to the area of 6 tatami mats, 12 x 12 Japanese feet square, or 142.3 square feet (13.2 m²).^[b] Some of them are found concealed inside a shell.^[3][4]

One source (Tokihiko Ōtō [ja] 1949) identifies the locality of the lore as Sodeshi [ja] village,^[4] which is on the northern tip of Tango Peninsula [ja] (aka Yosa Peninsula). The localization is given more vaguely as some promontory area in Yosa District, Kyoto.^[2][3], and the yōkai is also described as appearing in Wakasa Bay.^[6][c]

An actual marine animal compared to this yōkai is the Common blanket octopus (Japanese name: murasaki-dako, lit. 'purple octopus') that inhabits the Sea of Japan. It has membranes between the tentacles when outspread can expand its area 10-fold, though the octopus is quite small.^[6] This octopus is in fact called koromo-dako (衣ダコ) locally in some areas of Japan such as Takeno, Hyōgo.^[7]。

A similar creature described in a collection of sea yōkai is the Futon kabuse (フトンカブセ; "bedcover coverer") in the lore of Saku Island [ja], Aichi Prefecture. It is said to arrive waftingly, encloak its victim in zip, and suffocate it.^{[d] [4]}

Julie Kagawa's novel Night of the Dragon (2020) mentions koromodako, ushi oni and umibōzu in the same sentence as creatures one does not wish to encounter at sea.^[8]

• Argonauta hians (Japanese name: tako-bune - a shelled cephalopod, aka winged argonaut, muddy argonaut or brown paper nautilus
• Cuero (legendary creature) - legendary "hide/leather"creature of Brazil, aka Manta ("blanket, cape"), with octopus origin hypothesis