I was under the impression that Chang'e drank it first. Kaguya is said to have lived for at least 1300 years, whereas Rei'sen (Reisen II) stated in CiLR Chapter 6 that they've been "pounding away [for Chang'e] for thousands of years." If we go by their actual legends, Taketori Monogatari is from the 10th century. As for Chang'e's, I can't find a time range, but the Guizang text contains a story of her, and it is said to "had been lost for roughly two thousand years."
It might've been just hyperbole. After all, the Elixir wouldn't exist at all if not for Kaguya's whim. I don't think Eirin would've completed it and then given a sample to Chang'e before giving it to Kaguya.
Actually, I just found out that Chang'e really is the Chinese goddess of the Moon. But to answer your question, that could also be true. However, if Rei'sen's thoughts are to go by, they don't seem to give much thought to their mistress... They treat the pounding now as mere routine.
She's the Goddess of the Moon in chinese mythology, yeah, but that doesn't necessarily mean that she's the same here. Also, Junko's profile does say "[Chang'e] rules over the moon rabbits", so I'd guess that this is her primary function here.
Maybe they just care that she's in the moon at all? Or maybe they become useless if she's away from them. Well, we don't really have much to go on here.
Now for something unrelated:
I've been trying to figure out why the Lunarians couldn't actually fight back against Junko's plan...
It seems, going by Toyohime's fan, that the Lunarian weapons are based around purifying impure things, which appears to completely destroy them. Since any other kind of death would invite impurity, I assume they don't actually have weapons that don't work this way. Therefore, since Junko purified the fairies to turn them into "pure lifeforce", the Lunarians weapons would be unable to do anything against them, since they aren't impure at all. And of course, killing fairies in general is impossible since they just respawn, so any other method of getting rid of them would be useless. And furthermore, since they are basically terraforming the moon, it's too risky for the Lunarians to even try to leave the capital.
Does this make any sense?
At any rate, thinking about this made me realize just how hilarious the whole situation really is. The Lunarians, supposedly the strongest race in the Touhou-verse, were basically nearly completely defeated by a bunch of
goddamn fairies.
where are your gods now, yorihime :V
