Umi bozu

Perhaps no other aquatic yokai is as mysterious as the giant umi bōzu. Their true form is unknown, as they are only ever seen from the shoulders up, but they appear to be roughly humanoid in shape, with inky black skin and a pair of large, round eyes. Eye-witnesses report a great range in size, from slightly larger than a ship, to a size so unimaginable that only the creature’s bulbous face is visible above the water. Its head is smooth and round like that of a venerable monk, and its body is nude and as black as shadow. Some reports make them out to be more serpentine, while others make them out to be more ghostly, like a gigantic kind of funa-yūrei.