I believe you've talked about this in another comment but I do want to bring this to your attention again, the subject being the St. Viviene fight. remembering my own struggles with this, I decided to give fighting her on a maxed out file a try. the result was having a hard time beating her one level below the maximum (which I believe is 8) and feeling a burning need to post this. to max the save file, I fought the same ghoul over and over again until it dropped a vampire dust, making a mistake here and there, losing a total of 3 vampire dust before the fight. overall, I just want to say that the fight's balancing is a huge issue for new players not expecting the difficulty of the fight, and the fact that you played the whole game beginning to end to address issues like this is extremely admirable. I wish you have a great time developing this game moving forward.
Update on this situation: the max level at this point is like 10, not 8. and I was level 9 at the time of the battle. but other than that, I just wanted to say that the main thing that bothered me about the boss fight was not the difficulty of the whole fight, but rather the ridiculous amount of damage she does with no warning in the final phase, especially considering you have no turns to prepare since you need to attack her for her to enter her final stage. The immense amount of damage she deals makes it so that defeating her at level 5-6 feels like gambling, just hoping that you land a critical hit, or that her bite misses. Some things I had in mind were a potential warning for the bite, or just outright reducing it's damage considering it deletes half of your max HP or more if it hits. Although generally the fight is fine: difficulty is good, and mechanics are great!