i have beaten the demo. i remember reading about how you felt like writing was giving you a hard time, and i can tell you that i greatly enjoyed what is there. i'll again refrain from saying anything too specific so anyone here doesn't get spoiled, but i think you tackled Enkidu's part of the plan well - he went and we as the viewers are left in the dark like the characters (instead of now playing as him or something similar).
so here's some bugs for you to get triggered by.
something to consider (that might be a pain) is a "back" button for next - to go back one slide. i did accidentally double press next and i wondered if i could go back ,but evidently not.
something about the game really doesnt like be using the windows snip tool. might be a new OS thing (11) but i had to mess around with it to be able to actually capture the screen. i don't think this is tied to the game (maybe godot?) but it's worth noting that screenshotting is hard.
Peter's attack sound is really weak compared to his visuals/damage/abilities. he's a big guy with a man-sized halberd/bardiche/naginata thing, and when he swings it it makes a weak swing sound. at least give him finn's blunt swing sound.
xanadu solider animation is a bit weak, noticeable when he's an ally. i think speeding it up x2 might fix it?
last level map (Finn / Gaz's side) is confusing. it feels like i'm zoomed in or that the bottom side of the screen is cut off.
Finn's attack is also slightly too loud when compared to everyone else's.
silly issue: i noticed Mosca got 1-turn-KO'd when faced with the first desert assassin encounter (For me it was assassin + 2 audience members). i also noticed finn was rather weak - until i realized they're level 1! probably something to do with saves or whatever, but they remained level 1 until i reached a holy ground and leveled them up. you probably wont ever have this edge case in the actual game, but perhaps a mandatory "level up" screen should be imposed on the player if the game detects a character is level 1 at a late stage of the game.
"...amount of champions increased geometrically" says the Taurian Knight to Finn. kind of a weird expression - does he mean exponentially? maybe i'm ESLing it.
at the last fight (for which the intro was very cool, by the way) - i killed 30 foes, which unlocked the dreaded 4th lane bug, where enemies started spawning beneath the bottom-most row. i didn't want to mess with it more so i bit the dust there. maybe you can reuse the timer mechanic, where after a certain time the fight auto-ends saying you held out long enough.
perhaps tied to the 4th lane bug, but ending the demo, your dev-avatar shows up and softlocks the game! he has nothing to say, auto/escape/next don't work either. my only option is to alttab and close it. i'll never know what message you may have had for us, a pity.
as always, you know what you're doing, so simply keep doing it.