I haven't counted how many times the first boss, lava spider dude, has handed me my ass. I want to punch a bag full of puppies and kittens right now. Go ahead and laugh.
I've figured out what I have to do to beat it, I keep whittling it down to one quarter of its life only to die. Over and over and over. I finally caved and tried the Easy/Auto option and hated it. It does all of your combos for you, dials down the health and damage enemies can deal so far down all the while it dials your health, damage dealing capicity and devil trigger so retardedly high up. It's so...patronizing.
I saved the Auto/Easy on a new file, reset and loaded up my original save file before the boss fight.