Saku (a Touhou LW original) refers to the new Moon or the first day of the month. This is an apt temperament for Sagume, the Lunarian in a nurse uniform, learning how to protect everyone's physical and mental health at the end of summer. "We need to administer medicine? Leave it to me, Nurse Reisen." (Strong against Fire Phase.) "A blood transfusion? I can handle that, Nurse Medi." (Strong against Water Phase.) "The nurse trolley flipped a full 180 degrees. How did that happen...?" (Strong against Earth Phase.) "Strange. I thought I'd be better at this. Hmmm..." ( Weak to Star Essence.)

The ability of Sagume Kishin from the world obsessed with healers (a Touhou LW original). This ability doesn't seem that different from the Sagume of our world's ability. In this world, the sweltering heat of late summer never ends. The seasons represent the cycle of life and death, and the Lunarians sought to escape this impurity, so they probably don't have any seasons on the far side of the Moon. Apparently, they forged their own independent civilization on the Moon, far from the four impure inevitabilities of human life: birth, aging, sickness, and death. However, this doesn't quite add up. If the Lunar Capital is free from all disease, why does Eirin Yagokoro have the ability to make medicine? That's really strange! Then again, medicine isn't only used to treat wounds and illness. The defining trait of medicine is that it directs the patient toward a specific state or condition. In this sense, it is no different from poison. Perhaps this is best understood by how some medicines can be used as cosmetics or for recreational purposes. Also, while the Lunarians have distanced themselves from impurity, it is fairly safe to assume that they are not entirely free from the sufferings of birth, aging, sickness, and death. Otherwise, they would not condemn the Hourai Elixir's immortality as something impure. Impurity comes from fixating on life and death. So, to wish for immortality is basically the same as declaring yourself impure since it implies you live in constant fear of death. Long story short, the people of Hourai are truly immortal, but while the Lunarians may live an exceptionally long time, they are still essentially mortal. That's why if the Lunar Capital ever becomes an urban heat island, the Lunarians might even suffer from heatstroke. Sagume Kishin was completely taken aback when she witnessed Lunarians collapsing in the sweltering heat one after the other. She had been learning a lot about medicine during her secret meetings with Eirin at Eientei, so she knew that the best prevention for heatstroke was maintaining a balanced diet, rehydrating regularly, and replenishing the body's electrolytes. The Watatsuki sisters also knew this, which is how they all managed to endure the oppressive heat. The other Lunar Sages accused Sagume, the Watatsuki sisters, and other members of the pro-Yagokoro faction of purposefully causing this heat by using knowledge provided by Eirin Yagokoro to terraform the Moon. They even demanded an investigation into the matter. However, the truth was that Eirin's imparted wisdom helped the Lunarians recover, and that the other sages' demands were merely a ploy to uncover the cause of the unusual temperament. Once everything had settled down, Eirin was awarded the Eirin Prize for Physiology and Medicine for her research into Astral Doors. This was purely an act of self-preservation by the other sages who cannot fulfill their duties without relying on Eirin, the Brain of the Moon. Lord Tsukuyomi won't take any reports seriously unless they're signed by her. Sagume, now with an Astral Door halo and wing, visited Eientei. At first, she had assumed they only managed to save the Lunarians suffering from heatstroke thanks to Eirin's wisdom, but that didn't explain how they recovered so swiftly. When she took these suspicions to Eirin, who she greatly respects, Eirin smiled softly and said, "That's the power of the Astral Door." Kaguya, Eirin's favored student, followed this up by instructing Sagume to let the Watatsuki sisters and Reisen, their pet, know about this, too. Then, one thing led to another, and Sagume became Eientei's new trainee nurse. Astral Doors impart medical knowledge from other dimensions, like how gods give humans divine revelations. But how it actually works is a mystery. It would be impractical for it to directly link with Sagume's brain through a physical interface, not to mention you'd be able to see the connection. So there must be some kind of wireless connection. Perhaps it's something like telepathy, where it uses electromagnetic waves, brain waves, or psychic waves to affect Sagume's knowledge and skills remotely. If that's the case, then who sends these signals from the other dimension? Sagume thought it might be Chang'e, the goddess of the Moon, who was locked up for drinking the Hourai Elixir. She's the ruler of the moon rabbits, so perhaps she can use telepathy through other dimensions to contact people outside her prison... But Eirin quickly shut her down, saying there's no way that's true.