[BlazingAbyss]

This was actually very helpful, thank you. I see that I was at least correct about those three being incorrect spellings of what they were intended to be. This actually makes a lot of sense since there's a fair amount of Latin words used here, Liber (or Librum as the game calls them,) Lumen, Tenebrae, Vesper etc.

I agree with you that they probably meant "Fossa." Despite this being the Aether's theme music which as the name implies is in the air, the stage boss of that area is some kind of half buried mummy thing so I can certainly see the correlation. Especially since the others seem to mostly have fitting correlations, like how Ignis is a phoenix for example. In addition, although Google Translate is obvious unreliable, when I use it to translate people talking about that boss, it comes out as "Deus Fosa" which seems far too similar to simply be confidence.

As for Lumen and Tenebrae I'm pretty sure they're just referring to how the last two paths you can pick from are Light and Dark themed.

As for "Kouk the Fire" I feel that Kouk may have came from the クク族 in 胸いっぱいのククを which would be Kuku or Koona in the English version.
Going by the liner notes for this song that RPGalaxy translated that mention that "Their feelings are on fire!!!" Maybe the proper translation would be something like "Koona on Fire!!"?

Also, I wasn't aware that the Japanese write "Encounter" as just "Encount." That's interesting, I've never come across an instance like that prior so I wasn't aware.