I am fairly certain it affects the mp drain (your soft time limit) and how much you recover from the enemies. Admittedly the platforming is still ass in that level no matter what you do.
But again I don't really have issues with the underwater section even on hard, it is just tedious and annoying to get through, not hard each time I run out of continues, it is escape afterwards that is killing me
You might try wearing lighter armor to help improve your mobility a bit (I wore the not-revealing-at-all angelic armor and that seemed to work pretty well). Also, getting a big sweeping weapon really helps against all the annoying little enemies that tend to knock you off.
You don't think this is light enough, that is more of less how I played the entire game btw
And as you can see there I am using the Elemental sword, not sure what you consider a "sweeping weapon" there don't seem to be one weapon that is particularly more "sweeping" than others, but mainly difference in speed and damage (with elemetal being the fastest attacking weapon, yet still 1-2 hit kills most non-boss targets, somehow...)
Also just to be clear, the crystal difference on hard vs. normal is not actually that significant. I would just beat that particular level on normal so you can get to the rest of the game, then maybe come back to it later. The best level to grind for gems is one right before the final boss, so getting there will help in prepping for endgame hardmode.
I honestly didn't know there was a crystal difference at all, don't think they game told that anywhere, I am playing on hard by default always when it comes to H-games simply because they tend to be WAY too low in difficulty even on hard mode often when such a mode exists, and for the most part until know I haven't had a lot of issues in this game either
Bingo. Just do it on easy and make it far enough into the pile of crates at the far left end before he kills you.
Fair enough, I'll try that, on hard you are pretty much guaranteed to die by the 2nd set of crates (and that is only because you can jump over the first single crate, trying to smash even that one will kill you)
EDIT: Yeah did chapter 13 on normal even, not even easy as you said, and felt like a freaking god during it... such a HUGE difference in damage you take... yeah I was right in playing on hard in general if that is how little damage you take untransformed even on easy difficulty...