So you've probably heard of this rare demo, maybe from the interesting ZUN art, or the lost spells that are not in today's PCB. If you've tried to find it on Google somewhere, you probably found nothing.
Well, after months (yes, literally MONTHS, ugh) of searching for this, I finally found it.
Mediafire download link. It contains an installer but it's not necessary, the game fully works with what's located in the "youmu" folder. (and also has omake.jpg which you should check out for some rough ZUN art)
There are several different things in this demo. If you don't want to know what they are yet and want to find out for yourself, don't read this next portion.
Sadly, you cannot use vsync for this game, so you're going to have to deal with the input delay. I at least recommend, for newer Windows OSs if you use Aero, that you check "Disable visual themes" and "Disable desktop composition" under the properties for the executable so the actual window doesn't bleed into the game. If you don't use Aero, it probably won't be an issue (I don't and it isn't a problem).
Also, a translation of the custom.exe would be awesome, as it appears to be different from EoSD's and PCB's current versions. I don't know if the conversations differ either since I can't read Japanese.
Anyways, have some fun with a demo that's been nearly impossible to find anywhere!