Glitches and quality of life:
First of all, I haven't gone past level 35 so I might not know all the skills available, but the player character should get a better multi hit skill around level 25-30 range because the multiple enemies that appear from the random encounters can get a bit tedious when going back and forth from the starting area.
Now the shop where the old lady stands is kind of confusing because first she offers to sell the player weapons and potions, but then when leaving the shop she tells the player that there's a discount on her things and if the player agrees then he will be able to buy a cheap armor piece. This was kind of confusing, because there wasn't indicator that she was selling armor and it took me a couple of minutes to realize that she sold armor. One last thing with the shop lady is when I read the description for the potion that increase the players sp, the problem with this is it was hard to understand it actually meant mana and also the word increase in the description made me think that it would increase the players mana, but it recovers the players mana by 15 instead.
I know this is a demo, but there are still many areas I thought I could go to, but couldn't. Maybe for the demo version of the game there should be barriers that prevent the player from going some way to not confuse the player.
The bed and campfire should also have indicators to them, showing the player that they can heal fully in these locations, like a fairy (or what ever would makes sense in the Zuex Of Zarlin world)
I noticed in the tent that there's a two way door out from the tent, which is fine, but when the players tries to go from the right side of the screen the player isn't able to leave, you can only leave from the left side, maybe make it so the player is also able to lave from the right side.
There was also a weird part in the swamp where there was a girl behind a stump, but I don't know if it's intended, but I can get to the location where the girl is by going from the left or right side of the stump, directly from the water. I wasn't able to interact with the girl.
When finishing the demo one of the text box text clips out from the box.
The other thing that would make the game better is if there was a consumable crystal that makes it possible for the player to be transported back to the starting area, just so the player doesn't have to move back and forth. (If there are other main bases in the game make some other crystals that make it possible for the player to transport there too)
Events:
I wish there were more events going on in the game, mainly cause from what I saw from the game it doesn't have a visual novel level of dialog, so the game falls flat on that apartment, which is fine, but there has to be more interesting events in the game to balance the lack of story or
the game won't feel like a living world. The duel in the beginning of the game and the mimic chest in the swamp are a good start, but there was too much time between those two events where much wasn't happening at all.
Since the game has many lizards in the beginning, how about if a certain amount of lizards are defeated a lizard king spawns in the game and for defeating it the player gets a egg that will open up around the end of the game giving the player a powerful party member.
When the undead bite the player enough times the undead won't attack the player anymore because they consider the player one of their own kind and if that happens the player will be able understand the undead language, but now instead of the undead the player will have to fight other adventurers instead, but the adventures will drop better gear then what is in the early game store. Although if the player has defeated enough adventurers an early ending will be available where the player can join forces with the undead to turn every being in to the undead, but if the player doesn't want that ending the player can choose the no option to make the undead enemies again and for a reward the player gets a
passive ability that gives him immunity to all status effects.
If the player defeats the first duelist other duelists spawn around the game and the first duelist will give the player a guest to beat all his brother in a duel and if the player is able to beat them all a legendary warrior will spawn to face the player and for defeating this warrior the player gets a knife that heals the players hp (maybe mana too) when it hits the enemy.
There could also be some flashback events where the player plays the events before the game began and if the player pays attention to the flashback and the player goes back to where the flashback event happened the player can find a weapon or armor in the place where one of the characters stood in the flashback. The flashbacks can also show the main character showing more of his personality and his motivations.
Over all it would still be good that all the events were optional, expect for the main story parts. Since the reason I enjoyed the game in the first place is that every location doesn't have forced talking to the player every second, and there's some down time of just battling monsters.
Story:
Since the game doesn't have a lot of story segments it would be good if the parts with the story would have more dialog to build the world of Zuex Of Zalin.
It doesn't have to be a bible of text, but there should be enough information in the main story that give small hints to the player that foreshadows the final battle.
I really liked the demo, hope you keep developing it.