Thanks for playing! Having a bit of knockback or something for the sword is a good idea.
I was going to point out that energy gain rate was based on Hollow Knight, but after going back to check the values for that game I'm realising that I must have mixed up the hits to fill a soul vessel with the hits the to fill the soul meter. Which probably means nothing if you haven't played it, but the point is that the energy gain should be a lot higher. Will have to try increasing it in future updates.