Onibi

Onibi — "demon fire" — is the umbrella term. It's the class, not a creature.

And the definitions the record gives are two, which is useful:

Fires born from the corpses of humans and animals.

Or resentful people who have become fire.

That second one is the distinction worth holding. There's another kind of ghost- light in this tradition — the hitodama, the soul-light, which is a soul in transit, drifting out of a body around the time of death and going where souls go. That one is sad, not hostile.

The onibi is combustion with a grudge.

What they look like

Blue. That's the signature colour, and it's the whole point — because hearth fire is never blue. Cooking fire is orange. Lamp flame is yellow. Anyone who has spent their life around domestic fire knows what fire looks like, and blue isn't it.

Also recorded: bluish-white, red, yellow.

Sizes run from a candle flame to several metres across.

And they float, characteristically, one or two metres off the ground — head height. Not up in the air, not down on the earth. Exactly where a person's face would be.

When they come

Spring and summer. And — the detail that does the work — on rainy days.

Which is precisely when honest fire struggles.

That's the rule underneath the whole class. A fire burning in dry conditions is just fire. A fire burning in the wet, easily, at head height, in the wrong colour, has declared itself.

Wet fire is wrong fire.

Where they come

Wetlands. Graveyards. Waterside.

All three are the same kind of place — ground that is neither properly land nor properly water, which is the sort of boundary this tradition puts everything on.

And they come in swarms. The record has twenty to thirty at once.

They're not all dangerous

This is the honest complication, and it's what makes the class a class rather than a monster.

Some traditions have them draining life. Some have them merely appearing — they're there, they're wrong, and nothing happens.

And Kōchi has the asobibi — "playing fire" — which is explicitly and entirely harmless. Lights that come out and mess about and go away again.

A whole region looked at the same phenomenon and concluded it was having fun.

The family is enormous

The fire-lights are the largest single family in Japanese folklore, and the named members each carry their own story.

There's the oil-thief monk of Kyoto, still burning as a flame because he skimmed the temple's lamp oil. And the oil-thief crone of Osaka, doing the same, appearing as a fire with an old woman's face in it.

There's the fox-fire — kitsunebi — lines of lanterns crossing hillsides in processions no one is holding.

There's the great light over the sea at Yatsushiro that gave a whole province its name. There's the cold fire on your raincoat that multiplies when you brush at it.

And then the long catalogue tail: fires at wells, fires that drift, fires on old battlefields, fires at graves, fires with a heron in them.

They're all filed here.

And the science won't resolve it

There's a standard list of explanations and they've all got something going for them.

Phosphorescent decomposition in wet ground. Phosphine and methane igniting over marshland — the classic will-o'-the-wisp mechanism, and it fits the wetlands and the graveyards uncomfortably well. Plasma and St. Elmo's fire, for the ones near masts and points.

But the record's own conclusion is the right one, and it's admirably unsatisfying:

"Onibi legends themselves are of various kinds."

Meaning: this isn't one phenomenon. It's a category people put things in. Marsh gas, static discharge, a distant lantern, a misjudged distance, a bird with luminous fungus on its feathers, and a certain number of nights where somebody saw something and never found out what.

One explanation was never going to cover a filing cabinet.