Apparently this requires a "program ID" (probably CD Key) to install? Is a crack or a usable key included?

Don't install the game. Mount the ISO or open it as a zip archive. Take out only the folder called nine. Now go to mikocon make an account and download the 2D crack at the bottom of the OP. replace nine.exe in the folder with the crack.

For anyone who'd like to install/crack, I wrote a blog to introduce the method. You can use google translate to translate the page and follow the steps. https://blog.mmf.moe/post/9-nine-pkutil-reimplement/

Thanks for this! English here! https://nyaa.iss.one/view/1503978

The crack download link on the mikocon forum is dead. I was able finally bypass it after google translating the guide from @Yesterday17, but MTL is vague and hard to understand, so here's the gist of it: 1. Download the crack files at the bottom of his blog page from google drive 2. When you're installing the game and it asks for your key, put a bunch of random numbers 3. Move the install window aside for a second and go to your computer's %temp% folder. Search for nsispkc.dll. If it doesn't show up then refresh the folder and search again. Replace it with one in the crack folder. 4. Go back to the install and try random numbers again. It should let you finish the install. 5. Go to the installed game folder, and inside the plugins folder you need to replace pkutil.dll with the cracked one.

I just found out that this version is all-ages...