the difficulty difference between the first beatable boss "ishumi" and the second one "yumeko" are several magnitudes. you can beat Ishumi with no items no mp use and lose around 400 hp average. where Yumeko is so difficult I had to quicksave and grind the blue flame in order to get the gear levels and money to even have a chance at beating her. and even then its more luck than skill. her qte move is glitched at least in my game where its a 1 hit kill even if you successfully struggle and have a significant amount of hp. which really sucks because her normal attacks hit so hard you either need a significant amount of hp or an abnormally large amount of health pots and mp pots to even survive, or pray to rnjesus that you pass enough qte and that the qte happen frequently enough that you can heal up. also there isn't enough damage difference between a basic punch and a bronze strike for it to be worth it most times due to the miss chance.
all that said i hope you continue to improve. i can see you put a lot of time and passion into this game. and i know there are several features not many have found yet. (due to me finding them through a glitch that i dont know how to repeat but when i do ill let you know how.)