I can only assume there is a difference, however subtle it may be, between using よ or さ as a particle at the end of a sentence, but I really don't know exactly.
In practice : I was listening to the song Nevermore from Persona 4, and I always noticed that, in the lyrics, the singer says throughout the song "暗い闇も一人じゃないさ" (like at 1:18 for example), except *one* time where she says "暗い闇も一人じゃないよ" (at 4:38).
I want to believe there *is* a difference, otherwise why would it be a thing (and it's not like it's an ad-lib mistake, in every alternative version of the song, every live concert, etc., it happens), and the only thing I can notice is that, the moment she uses よ, the song is a little more quiet and mellow with nothing but her voice and beats so maybe it sounds more… "intimate" ? Every translation of the song I've found, there is no difference in meaning whether she uses よ or さ, but at the same time, I know it's extremely difficult to render the subtleties of particles succinctly of course.
Would you say her using よ or さ is significant in meaning ? Does it maybe tinges the sentence with a different implied emotion ? Does it make sense to you that she uses よ in one place and さ in another or is it looking too hard into it ? Thank you in advance for any help you may provide
by FwooshingMachi