So, how exactly do the Lions work in Quintenary Stars?

You mentioned that they’re the physical manifestations of the five colors of Quintessence, but they’re also very clearly machines that can be modified as shown when Pidge retrofitted Green with the invisibility tech from the labyrinth.

Do the mechanical shells simply house what you could call the “souls” of the Lion?

I haven't really figured out how the lions are mechanical while still Pure Quintessence yet (tbh maybe their mechanical bodies Were built but their Essence wasn't ?? idk. I'll have to think about that) BUT yeah <3 the lions' Essence or Core or Soul or whatever you wanna call it is the entity living inside the physical mechanical lion and bringing it to life. the lions have a metaphysical form that they appear in while inside the spiritual plane (that can only be reached by the paladins via meditation/close connection with lions) OR to the paladins in the physical world when their bond is strengthened enough. the lions' metaphysical forms can be visible to other people who aren't paladins, but it depends on the temperament of the lion herself whether or not she willingly Shows Herself to other ppl (black or red, for example, are much more reserved and won't appear in their metaphysical forms unless they're alone with their paladin/paladin's closest + most trusted family, but blue is much more outgoing and will show herself to just about anyone. the only requirement for the metaphysical forms to become a possibility is an extremely powerful lion/paladin bond). the lions can also physically fight alongside their paladins in their metaphysical forms but again, the bond has to be really tight

but yeah once the paladins develop their relationships with their lions enough, they'll eventually be able to literally pet and play with their lions <3