Sazae-oni

A turban snail — the spiral sea-snail you get grilled in its own shell at seaside stalls — reaches thirty years old and becomes a demon.

Thirty being a very long time to be a snail. Roughly its century.

And it can unfurl out of the spiral into a woman, when it needs one.

The pirate story

This is the tale, and it is the bawdiest thing in Japanese folklore.

A pirate ship finds a beautiful woman drowning, and hauls her aboard.

She recovers. She is grateful. She is extremely grateful.

And over the course of the night she seduces the entire crew — and severs and collects every man's testicles.

When they discover this, they throw her overboard.

She surfaces in her true mollusc form, holding the collection, and makes an offer.

Your treasure for your jewels.

And the pun seals it

The word for testicles in Japanese is kintama.

Golden balls.

So the trade is: gold for gold. An even exchange, honourably proposed, in a transaction where both commodities are precious metal by name.

The pirates pay.

They hand over the ship's treasure, get their property back, and — one presumes — sail off having had the single worst commercial night of their careers.

Note who wins

Because that's the part that makes this more than a dirty joke.

It's a heist story, and the sea-woman scams the scammers.

Pirates — professional takers, men who board other people's ships and relieve them of their valuables — are separated from their entire treasury by a snail, using their own method: come aboard friendly, take what's portable, negotiate from strength.

The tradition's folk humour at its most cheerfully savage, and the moral, if there is one, is that greed and appetite are the same lever and she pulled it once.

There's a darker variant

Coastal inn tales, where the sazae-oni is a guest who arrives at night, devours the innkeeper, and slips out at dawn.

No pun. No trade. Just a lodger who was something else.

The comic and predatory registers coexisting in one creature, which is entirely normal here — this tradition almost never commits to a single tone, and the funniest monsters usually have a clause like that further down the page.

Where it comes from

Sekien, 1784 — and the placement is doctrinally interesting.

The sazae-oni plate closes his first volume of the tsukumogami catalogue — the book of objects that come alive after a hundred years.

Umbrellas. Sandals. Paper lanterns. Tea kettles. Musical instruments.

And then, at the end: a shellfish.

Which extends the doctrine in a way nobody had bothered to state. The rule was supposed to be about tools — made things, used and discarded, acquiring a grievance and a face.

Sekien quietly applied it to something that was never made at all, on the grounds that thirty years is a snail's hundred.

The threshold isn't a number of years. It's a full life's worth, whatever that is for you.

Which means the animate-object doctrine is really an age doctrine, and Sekien demonstrated it by putting a snail at the end of a book about umbrellas.