The mistress of the Saigyouji family who resides at Hakugyokurou in the Netherworld.

It is said that she died over 1000 years ago, so she is a ghost with an abnormally long lifespan (*1).

Impressed by her unwillingness to hold grudges and her ability to control spirits, she was appointed by the Yama to manage the souls of the dead.

In return, she was permitted eternal residence in the Netherworld.

Her appearance is no different from those of humans.

It is said that the color of her skin and hair is paler than when she was alive.

As her body is sealed away within Hakugyokurou, it is said to be impossible to hold a burial ceremony for her.

Thus, she will live (*2) eternally in the form of a ghost.

Her personality is so extraordinarily carefree that it is said she doesn't remember how long she's been in the Netherworld.

It seems she doesn't even remember what she had for breakfast (*3).

1: "Lifespan"?

2: "Live"?

3: Perhaps senility is setting in.

The ability to manipulate death means just as it says, the ability to kill someone with no resistance.

Once they're dead, she would be able to control their spirit as well.

Nothing good can come out of challenging her.

Her father was a widely adored poet, and eventually fell into eternal rest beneath a cherry tree as he wished.

His adoration continued after his death, and now he has ascended into heaven as a god.

Every year some grand personage would die beneath that tree when it was in full bloom, just like Yuyuko's father.

The tree continued to absorb their blood. It turned into a youkai cherry tree with the ability to lure people to their death, and it became to be called the Saigyou Ayakashi.

It is said that the Saigyou Ayakashi is now kept in Hakugyokurou in the Netherworld, sealed with the bodies of countless people, including Yuyuko, who sleep beneath it.

For this reason, it never reaches full bloom. The Ghostly Emigration Project

This is a story of twenty or thirty years ago.

The number of spirits in the Netherworld increased due to limits on ascension (*4).

Gradually, the already-vast Netherworld was becoming overcrowded, so she allowed them to inhabit various places (*5) in the world of the living as they were waiting to reincarnate.

The places she chose included closed schools and hospitals, abandoned buildings, and places people don't usually visit, but some curious person on the outside caught sight of one of the ghosts, so people started flocking to these places (*6).

Eventually, the Yama became aware of this plan and decreed that ghosts shouldn't be seen, so it was put to rest.

Finally, the Yama increased the size of the Netherworld, thereby removing the necessity for the emigration plan.

It's said that the Netherworld today is larger than Hell.

4: As the heavens receive all those who have broken from the circle of transmigration, they've reached their capacity.

5: Including the outside world.

6: People like mysterious places.

"Hmm, maybe I should check out the Netherworld for the flower-viewin' party this year, too..." (Marisa Kirisame)

The flowers in the Netherworld are extremely popular even among the living.

"Cleaning up a place with that much space would be awful. Still, it must be nice." (Reimu Hakurei)

It seems the housework is left to the phantoms.

First of all, you will likely not meet her under normal circumstances.

She stays in the Netherworld most of the time, and if she has business in Gensokyo, she usually has one of the phantoms go in her stead.

However, there is one exception.

You can speak with her after your death.

Normally when you die, after you travel down the Road of Liminality, cross the Sanzu river, and receive the judgement of the ten kings at Higan, even if you've done no wrong, you go to the Netherworld and await reincarnation or enlightenment.

You will definitely see her there.

Surely something dreadful will await you if you manage to incur her wrath.

She will command her servant Konpaku to sever the circle of transmigration with her sword, and if she sends you back to Higan, you'd surely be sent to Hell.

It's probably best to read about her before you die.