Hyōsube

Kyushu's version of the kappa, with everything charming taken out.

The hyōsube is child-sized and lives in underwater caves. It's covered in thick greasy hair. It has a grin that the old plates render as pure malice, and it is a pollution creature rather than a drowning one — which is a genuinely different kind of monster.

It uses your bath

That's the signature. The hyōsube gets into the bathtub at night.

And what it leaves behind is the horror: the water afterwards is fouled — stinking, and covered in a slick of greasy hair.

The accounts go further. Water a hyōsube has been in is contaminated badly enough that horses that touched it died.

So this isn't a creature that drowns you. It's one that gets into the household's water supply and leaves it dangerous, which — in a place where everyone shares one tub, in order of seniority, filled once — is a genuinely alarming proposition.

Don't look, and above all don't laugh

The two taboos are what make it interesting, and they're both about contagion.

Seeing it brings on an unexplained fever. And here's the part that matters: the fever spreads to other people. You looked at something, and now your household is ill.

Laughing with it kills you. If the hyōsube laughs and you laugh back, you die.

That second one is the purest version of a rule that runs right through Japanese folklore: the danger is in the response. The hooked-hair woman on the Ehime road can't touch you unless you smile back. The mind-reading mountain being can only be beaten by acting without thinking. Aka Manto's question has no safe answer, so you give none.

But the hyōsube's version has an extra cruelty in it, because laughing along is involuntary. Smiling at a woman on a road is a choice. Laughing when something nearby laughs is a reflex older than judgment, which is exactly what makes it a good rule to be frightened of.

And notice that both taboos are illnesses that travel. Look and you get a fever that infects the household. Laugh and it's fatal. The hyōsube is folklore about things you catch from other people — and it lives in the water everybody washes in.

Eggplant on a spear

Every kappa-type creature in Japan has its tribute vegetable, and the regional variation is one of my favourite small facts in this tradition.

The kappa takes cucumbers — floated down rivers with family names written on them, and eaten to this day as kappa-maki.

The hyōsube takes eggplant, and the delivery method is specific: a fresh eggplant, spiked on an upright spear, standing in the field.

Not floated. Not laid down. Presented, raised, on a weapon.

It has an anti-shrine

There's a shrine in Saga — Shiomi Jinja — that keeps protective phrases against the hyōsube. Not a shrine to it. A shrine that holds the words you need to keep it off.

That's living practice, and it's rare. Most of this tradition's protective knowledge has dissolved. Here there's an address where the countermeasure is maintained.

Nobody agrees where the name came from. One theory derives it from an old military title. One from hyō-hyō, the sound it makes moving down a stream. One traces it to a deity of the Hata clan, which would make this greasy thing in your bathwater a fallen god — a claim this tradition makes about a great many of its worst creatures, and is right about more often than you'd expect.