Oof my friend. Starting your game off with a difficult boss before any chance to test out the combat and get a feel for it is a bold choice. Even darksouls 3 which starts with Gundyr as a first boss has you fight a few weak enemies on the way. Difficulty isn't bad but you're going to lose a lot of players if you don't let them get a feel for the gameplay before having to grind through a boss battle. I don't know if the demo is the start of the game or if you cut some tutorial from it to keep it short, but I'd hate to see what looks like a unique and interesting game with a lot of love put into it lose its player base in the first 10 minutes.