Umibōzu are humanoid, aquatic yōkai that are many meters tall. They have dark skin and large, round eyes. Only its head and shoulders are normally visible with the rest of it underwater.

These yōkai usually attack on nights when the previously calm ocean suddenly becomes tumultuous. They are extremely dangerous, and will attack any ships they find. It kills sailors by either breaking apart the ship or by demanding a barrel from the sailors and then using it to pour water onto the ship until they drown.

The only way to successfully get away from an umibōzu is to give it a barrel that is missing its bottom. This will confuse the creature, giving the sailors just enough time to sail to safety. Unfortunately, very few people ever survive their encounter with this yōkai.

FUN FACT: There are a few proposed origins for this yōkai. Some believe it is the vengeful spirit of a drowned priest. Others believe it is simply a personification of large waves or other natural phenomena.

Examples in various media:

Unnamed Umibōzu (One Piece)

Umi Bozu, later rebranded as Giant Sea Phantom (Monster in My Pocket)

Swosh, known as Umibōzu in Japan (Yo-kai Watch)