If you want a bit of variety while streaming or as a bonus incentive for something, etc., you can play wearing the angel costume from the demo by simply copying over the file from the demo ISO (c002.ptm) and renaming it as c001. You'll have to extract/replace the file in Dolphin or GCRebuilder/GCFT. Here's the demo outfit file.
https://mega.nz/folder/JxdDWZjZ#snPaeogNYJt2vAC8gVcVLA
In-game screenshot:
Running this game while having to listen to these particular SFX (BOING BOING) can be grating, so here's a simple file swap to mute those particular SFX. Thankfully Gurumin's audio files are mostly grouped together in a logical order, so these were easy to find (they're all in the gse section). If you want to mute any other SFX or whatever, I used itmcnv.exe to extract the WAV files, muted them in Audacity, then used itmcnv to convert them back into .itm files. I tested it, seems to work fine but let me know if I forgot an SFX or whatever.