The live-in maid at the Scarlet Devil Mansion.

The only human who lives in the house where devils dwell and leader of the maids.

A mysterious girl who works in a place that normal humans don't dare approach.

Nobody had ever seen her before she started working at the mansion.

Furthermore, she is ever an ally of youkai, and is cold-hearted towards human villagers who visit the mansion.

This suggests that she might not be a human from Gensokyo, but rather one from the outside or a completely different world.

As she has no close relations with anyone in the human village, she is still shrouded in mystery.

She does come to the village to shop though, carrying a refined atmosphere around herself. She is never seen showing hostility towards other humans on such occasions (*1).

1: Though she appears to act outright hostile while at the Scarlet Devil Mansion, this is likely because she is acting in her capacity as security for the mansion.

She has the ability to manipulate time.

It is among the strongest of abilities for a human to possess, and is not something that can be learned through training.

Manipulating time allows one to stop the flow of time and let only oneself move, to slow the flow of time and let oneself move at incredible speeds, or increase the flow of time and change apple juice to apple cider.

However, it is generally rather difficult to revert things that have already happened.

Things that have been destroyed, burnt down, eaten, etc. can not be returned to normal even if time is reversed.

Reversing time only has an effect to the extent that things that have been moved return to their original position.

Effectively, you can say there is no reversing time.

In addition, her ability can be used to manipulate space, as well.

Slowing down time also means to contract space, and hastening means to expand it.

She uses this marvelous ability to perform a great many tasks such as cleaning, laundry and cooking.

Besides that ability, she is skilled in knife throwing and conjuration.

It's said she can pierce an apple on the head of a fairy maid 20 ken far above her in the sky.

With her tricks, she makes things appear in her hand which should have held nothing (*2).

2: Please refrain from making tasteless comments like, "That's because she can stop time."

The Scarlet Devil Mansion's policy regarding maids is quantity over quality, and they are somehow able to accomodate all of the fairy maids in their employ.

She is the only human maid among them, and as the head maid she gives orders to the fairy maids.

The fairy maids are mostly useless.

They are sufficiently occupied in cleaning their own uniforms and making their own food (*3).

About the only thing worth saying about these maids is that they basically have no pay or vacation, but they receive food and tea, and can do whatever else they please.

They are free to leave and regain their posts, as well.

The fairy maids' lives are comparatively comfortable, and if they can come to enjoy their masters' occasional impossible requests, almost none choose to run away.

In contrast, the chief maid's job is severe.

As her duties include cleaning the labyrinthine interior of the mansion, taking care of its selfish master, managing the useless maids, going out to buy supplies in the human village and making pointlessly gorgeous meals, she has no time to rest.

It would be impossible to do all this work alone without being able to stop time.

3: Their existence doesn't really matter. The reality is that the head maid does most of the jobs.

Since the maids at the Scarlet Devil Mansion receive no time off, they have no private life. Thus, her character is not well known.

It is unknown why she works in the house where devils dwell, and why the vampires trust her.

It appears that she is not being forced to work by the vampires.

She even seems to possess a certain degree of power in the Scarlet Devil Mansion, and can sometimes give orders to the vampires.

It's still unknown whether the vampires sought out the services of her extraordinary powers, or whether she herself asked for the position of head maid at the Scarlet Devil Mansion.

In addition, it is said that the name she bears now was given to her by the vampires, and is not her true name.

According to one theory, she was a vampire hunter from the outside world or another world (*4), and followed the vampires into the Scarlet Devil Mansion to try to slay them, but was defeated instead.

The reasoning behind this theory is that the silver knives she wields are those used for slaying vampires, and also because of the abilities the vampires possess.

She had left for a remote location to train in slaying vampires.

While she was skilled in defeating smaller demons, she had never tried her hands on a vampire.

However, she had great confidence in her powers, and thought she would be able to defeat a weakened vampire easily herself, and, setting out on a journey to slay vampires.

Then once she reached the Scarlet Devil Mansion, she saw the vampire there who looked so young but was surprisingly strong, and was easily defeated instead.

The vampire, wanting Sakuya's power for herself, spared her and gave her a new name, which also gave her a completely opposite fate (*5).

From that point on she immediately became the vampires' servant, and since she had strong abilities, she was able to reach the position of head maid and even take a right-hand position alongside the vampires.

Later, the Scarlet Devil Mansion relocated to Gensokyo, but she felt it clashed with the odd environment here (*6), so at first she resisted against the vampires and the humans of Gensokyo.

However, upon seeing the vampire whom she could not defeat easily beaten by a human from Gensokyo, and that they both got along as if nothing had ever happened afterwards, she slowly began to open herself towards those around her.

Nowadays, it seems that something has broken through her facade, and while she still allies herself with the vampires, she has been more proactive in encountering humans.

However, it's possible that the vampire who manipulates fate planned for everything to be this way from the beginning.

What do you think of that theory?

Also there are many theories such as ones suggesting she is actually a Homunculus, a zombie or simply just an eccentric, but the most widely believed theory is the vampire hunter theory detailed above.

She claims to be in her late teens, but this is unlikely judging by her refined manner and the level of her abilities. Rather, she seems to be a human who has been living for hundreds of years (*7).

4: For example, the netherworld, Higan, or the moon capital.

5: From name analysis fortune telling.

6: She already had made a strange contract with the vampires. Please see the section on vampires for more information.

7: Since she is also able to manipulate time.