Hatahiro

A woman sits at her loom, weaving, while her husband is away — and she is furious with him.

She weaves for hours. Days. And every hour of that repetitive, solitary, entirely silent work goes into the cloth, until what comes off the loom is not a bolt of fabric.

It's a snake.

And it leaves the house and goes looking for him.

Wrath by proxy

Compare this to the most famous transformation in Japanese folklore and the difference is the whole entry.

In the Dōjōji legend, Kiyohime is spurned by a monk, and she pursues him — and somewhere in the pursuit her rage overtakes her body and she becomes a serpent, crossing the river as one, and burns him alive inside the bell he's hiding under.

She transforms. She travels. She does it herself.

The hatahiro's woman stays at the loom. She doesn't chase anybody, doesn't change, doesn't leave the house. Her product transforms, and the product does the searching.

That's a different and rather colder idea about anger: not a possession that takes you over, but something you manufacture, slowly, with your hands, over a long period, while appearing to do ordinary work.

The loom is the perfect vehicle for it. Weaving is the most repetitive labour in the premodern household — hours of identical motion, alone, with nothing to occupy the mind but whatever the mind has been chewing on. Wind a grudge onto a loom for long enough and you get one long stored coil of it.

Sekien drew it in 1784, and the pun-scholars have found his signature. One reading has the name playing on a stock theatrical phrase for a serpent's length, with the word for "loom" as the pivot. Another finds a homophone doing the work directly: jashin meaning "wicked heart" is pronounced identically to jashin meaning "serpent body."

The wordplay is the transformation mechanism. The wicked heart and the serpent body are the same sound, so becoming one is only a matter of which characters you write.

The real thing underneath

There's no confirmed folk tradition of cloth turning into snakes — this looks like Sekien's invention.

But he built it on something real, and the real thing is better.

Japan has legends of the *hataori-buchi — "weaving-sound pools." Deep pools in rivers where, if you stand at the bank, you can hear a loom working underwater.* The clack of the shuttle, the beat of the reed, coming up through the surface from something down there that is weaving and has been for a long time.

It's usually attributed to a water-deity, and it is one of the eeriest images this tradition has produced.

So weaving and water-serpents were already neighbours in the Japanese imagination, long before 1784. Sekien didn't invent that association.

He just introduced them formally.