It's not hard, it's just what Kh2 was originally supposed to be.
Kh2 essentially didn't have shit on Kh1's difficulty.
It's just a test of trial and error on lvl 1 critical.
I-frames are when you're temporarily invulnerable; if you guard, dash, dodge roll, aerial dodge and there just so happens to be an extra hit coming at you before the animation is finished it doesn't effect you. True your cursor turns red for a second but you take no real damage.