Reddit user the_mock_turtle has provided me a download link to a demo I had assumed to be lost, after seeing my reddit post asking about it.
Here's the download link: https://www.dropbox.com/s/11x06lb1busbvsl/guardian-spell-demo-all.zip?dl=0
The user: https://www.reddit.com/user/the_mock_turtle
The VNDB entry: https://vndb.org/v14788
My original post: https://www.reddit.com/r/visualnovels/comments/hktuop/link_to_download_the_guardians_spell/
Sorry if I broke any rules, I'm new to this site.