Sakuya Izayoi is a maid and the sole human working at the Scarlet Devil Mansion. She is also charged with protecting its owner, Remilia, who would be hard-pressed to find another as talented and loyal as Sakuya.

The reason she is able to complete such an astounding amount of work on her own is thanks to her ability to stop time. Supposedly, with time stopped, Sakuya's movements don't even kick up any dust.

Sakuya's ability to manipulate time allows her to stop time and move about freely or slow down time and appear as if she is moving at high speed. She can also use her powers to speed up time and create vintage wines in a flash.

Outside of very specific circumstances, it's hard to undo something that's occurred. Turning back time equates to returning anything and everything that moved to their starting positions. The reason the Scarlet Devil Mansion feels so vast is not due to some cheap parlor trick, but is thanks to Sakuya using her ability to influence the space within the mansion.

Sakuya may have abilities that set her apart from humans, but she is still very much human. During a past incident, Remilia said the Hourai Elixir is stored in the liver of humans who have gained immortality. But why would she know that? It may well be because she wishes for Sakuya to become immortal. One wonders what Remilia thought when Sakuya told her, "I'll be a mortal human as long as I live. Don't worry, though. We'll be together as long as I'm alive."