I thought I was en route to the Half-Mystic ending in this playthrough (having equipped and used my Mystic powers and rescued Gina), but I guess I was wrong because the game gave me the "Full Mystic" one. I tried redoing the battle in Half-Mystic form, but I still ended up with the full Mystic ending. I'm not really sure how the multiple endings are supposed to work, so I'll just link all three of them below.
Human ending, "As it should be"
Half-Mystic ending, "Paradise found"
Full-Mystic ending, "Asellus the tyranness"