The Lunarians are another important faction in Gensokyo. Well, a couple of them are in Gensokyo. The rest have their own place on the moon, sealed off similarly to Gensokyo. The ones in Gensokyo got kicked out from the moon because they weren’t pure enough.
“Hold the fuck up,” you say. “Not pure enough? Are they moon Nazis or something?” Well, no. What they mean by impurity is something they can actually measure. Think of it roughly as “impure” = “associated with life and death”.
“Well, okay, but isn’t kicking them off the moon for that a little harsh?” Well, strawman, the whole reason they live on the moon in the first place is that it’s about the least impure place they could find. Living in a pure land has many proven health benefits, such as softer skin and eternal youth. So, they understandably didn’t want that getting messed up.
“But what did they do that was so impure in the first place?” I’m glad you asked, strawman. Eirin, the smart doctor lady, made an elixir of immortality by borrowing power over eternity and the instantaneous from Kaguya, the NEET princess girl. “Hold on, weren’t they already immortal?” Good question, strawman, but living in a pure land only made them unaging, not immortal.
Strictly speaking, the Hourai Elixir confers not immortality, but amortality. It makes the victim’s existence completely independent of life, death, and even reality. In other words, the concept of life or death no longer applies to that person. Go ahead and ask, strawman. “But if the concept of life and death no longer applies, isn’t that as pure as you could get?” Thanks, strawman. Actually, it’s as impure as it gets. A person of Hourai is heavily associated with life and death by their complete absence. Thus, they are considered impure.
Anyway, Kaguya and Eirin became too immortal so the other moon people kicked them off the moon. Later, Mokou the depressed fire lady also used the Elixir, and some time later Reisen (sounds like “Raisin”) the moon rabbit ran away from the moon (well, deserted from the moon army) and also lived with them in their bamboo shack. Then they made the moon look funny and Reimu beat them up.
So why am I talking about this impurity thing? …Whoops, sorry to steal your job, strawman. There are a number of comparisons to be drawn from this concept of impurity and the events stemming from it. I’ll start with the most obvious: Pollution.
From the standpoint of impurity being analogous to pollution, the Lunarians kicked them out because they were using big, gas-guzzling, smoke-spewing trucks in their community of bikes and solar cars. (The trucks also made them immortal.) They couldn’t just take away the trucks because… um, this metaphor is set in the world of Pixar’s Cars, so they are the trucks. So they evicted them instead.
“Wow,” you say, “that metaphor got stretched hard.” Yes, thank you strawman, I know, but it does illustrate my point if you can suspend your disbelief. From this perspective, the Lunarians were fully justified in kicking them out. If your city… If your autonomous city-state populated by talking solar cars on the moon was working fine with just renewable energy, and then some asshole decides to make herself into big truck that burns dinosaurs and spews pollution everywhere just so she can go faster and be immortal… Well, you’d probably take a long, hard look at your life and wonder why you’re a talking solar car on the moon. But aside from that, you’d probably kick them out.
Religious intolerance and hypocricy
From another point of view, Kaguya and Eirin were kicked off the moon because they failed to follow a particular tenet of the dominant religion. Impurity, or kegare, is actually a central concept of Shinto, although here it’s sort of mixed with Pure Land Buddhism.
From this perspective, kicking them out was kind of a dick move. Sure, it could have been worse – they could have been stoned to death – but it was still kind of a dick move. (Well, they actually did execute Kaguya. Repeatedly. It just didn’t stick, for obvious reasons. Still a dick move.)
Worse, they didn’t even follow this policy consistently. Kaguya was repeatedly executed and finally banished, but Eirin was not punished at all despite having made the Elixir for Kaguya and having used it herself. This was probably because she was important, being the smartest person on the moon and having built the lunar capital. (Kaguya was also important, being a princess, but I think they just saw it as an even worse crime because of that.)
“But–” Yes, strawman, I was just getting to that. Eirin felt bad about not being punished while Kaguya was and was pissed at the hypocrisy, so she banished herself and went to go hang out with Kaguya. I simplified it for brevity earlier, and am actually still simplifying it here because it’s not really the main topic.
Anyway, this hypocrisy shows that the Lunarians’ artificial “pure land” would be just fine with a few people of Hourai around. In fact, they have another person who drank the Hourai Elixir, Chang’e, sitting around in moon prison. (That’s basically all that’s known about Chang’e, by the way.) So Kaguya being there wasn’t doing any actual harm.
So with this in mind, the Lunarians were sitting there, drinking their gluten-free carrot juice and relaxing on their moon beaches (by the way the moon has beaches), and being insufferably smug about how much more pure they are those filthy earthlings. Eirin and Kaguya had a barbecue, in which Eirin cooked but Kaguya brought the meat. The smug moon vegans then kicked Kaguya out of their exclusive moon country club and also the rest of the moon, for not being a good enough Muslim and/or just to be smug about it.
Curse of Hourai – Contagious Immortality
From a third perspective, creating the Hourai Elixir was illegal for a very good reason: It’s a weapon capable of inflicting literally infinite suffering. While I don’t think that’s the reason they had in mind, it’s a very good one.
A Person of Hourai cannot die. This Curse of Hourai is absolute and irrevocable. When the Earth and the Sun and the stars are all gone, the victims of this curse will remain, floating alone in an endless, lightless void for all eternity.
Eternity is a long time. Infinitely long, in fact. If you took the lifespan of a Person of Hourai and divided it by the lifespan of the universe, you’d get zero. Skipping to the conclusion, it’s the worst possible fate for anyone.
So why punish the victims? Well, the Elixir remains in their guts, meaning anyone that eats their guts will suffer the same curse. While this isn’t especially likely to happen by accident, it’s a finite chance for infinite suffering, which works out to infinite risk, so it’s best to get them as far away as possible just in case. Besides, it’s not as if it matters to them whether they’re banished or not – in the long run, nothing you could possibly do to them can actually make their
lives existences any worse.
Above all, though, you’d want to make sure they don’t go around making more Elixir anywhere near where you live. Thus, kicking them off the moon. Although, of course, this explanation still doesn’t forgive the hypocrisy.
Why they didn’t do it for any of those good reasons
The thing that really shows that banishing Kaguya was a decision made out of outrage rather than logic is the fact that, a couple of years later, they sent some emissaries down to Earth to tell Kaguya “Hey, we were just kidding about that whole ‘banished forever’ thing, you can come back now.”
Either they realized how dumb and hypocritical they had been, or people started complaining/they wanted something from her/some other selfish motive. Since these are the Lunarians we’re talking about, and they’re better than everyone and can do no wrong, it was most likely not the former. As it turned out, there wasn’t much time to find out, because she didn’t stay long.
Kaguya shrugged, went “Okay, I guess,” and returned to the moon. She then realized it sucked and she liked Earth better. So Eirin, feeling bad about not having been banished, killed all the other emissaries and brought Kaguya back to Earth.
Oh, and when Kaguya went off on her moon vacation, this girl Mokou, who was mad at Kaguya because she rejected her dad, decided to get revenge by stealing the Hourai Elixir Kaguya had given the random people she’d been staying with. Mistakes were made all around. Mokou, at least, realized almost immediately (a few hundred years) that she’d fucked up, but you know what they say about hindsight: You should have had it sooner. They later amused themselves by fighting to the death repeatedly and wishing it would stick.
And now you know most of the relevant bits of the history of the Moon. Well, not really, there’s a bunch more, but whatever.