Really fun game!
You did really well implementing the souls like style and I really enjoyed playing your game.
Overall, I think it would fit the style a bit better if you are not supposed to just go into the lake to finish the game. You don't need to be strong to do this, you could just rush trough all the enemies. Maybe add a wave system where enemies get stronger over time and you need to kill a certain boss to get some medicine to get rid of the parasite. Also, maybe the grub doesnt want to get rid of it as it gives it really cool powers.
Still, really good game and I really enjoyed playing it!