I got three paradise keys using thread search here, most annoying was first one because I was too stupid to try to press button even when not prompted (also had problem with furry route secret key because of that).
And then after beating secret boss I go looking for last paradise key. I know approximate zone when it should be located thanks to thread, again. And when I come close I see sparkles! I guess I should have started with figuring out boss and only then starting to look for keys.
btw I extracted audio and music and just by filenames I see they are taken from different sources, but in groups of 2-5 files, judging by prefixes. I've been looking specifically for chapel day theme and secret chapel boss. Filenames are 05myuu_Angel_Rasiel2 and 07myuu_Angel_Elijah. Looks like they are from same composer/circle/ provider. And I'm curious, whether he just got them from another game or something? Maybe this is reason they are not present in gallery, in order to not attract attention to fact