Hey there i check out your demo and all was fine as a battle system as you say, in that aspect i think more restore HP abilities needs to be implemented during combat, also just 3 weapons, could be nice if you look at ocarina of time or something and give weapons with abilities that could be cool, is a suggestion.
For the demo as a demo, i think you should try to focus more on others aspects like history, character development and stuff like that, the music on the game is ok but it could have better music, i do not use that kind of resources but as can i see in other games there is not much variation in the interior map, i mean i cool but every game i have played with that title set seems equal, the game progression and the duration is important too, and fix a beginning and end to the history, a lot of demos actually have that problem that you do not know where the game demo ends and stuff like that, the quest systems seems promising, and i love the rune stuff also.
I really want to know why a lot of users that use the script of the battle system are too focus on it and talk as if were something special, is hard say what kind of things are made by the developer and which ones are form the scripts, but all the games that works with that specific type of resources are too focused on that, I wonder also how many maps do you want to put in the full game, is cool that there is not random encounters and you can avoid enemies but that is also another problem because the variation of them, how many would be available for your game?, and the history is important too, the only thing I see of history “on the game” out the beginning is the quote under the character status, there are a lot of things you can use for your game that works well with the maps and characters give them skills to interact with certain objects are cool but the most is the quest system, a progression of mission that could have the player moving on.
I review you game as a demo and like that is more like a battle testing, the last boos is too hard to beat maybe impossible and if that was the intention then is cool, but if you are just trying to make a player test your game do not put bosses like if there was a complete game or challenge unless that is all of the demo, and if that is the case there is not much relation on make it hard to beat since is a test the player will not feel the necessity of continue playing numerous tries, I couldn’t find bugs at all but there is just a pair of maps so it could become more complicated or more substantial.