He is the easiest of the end game bosses as long as you clear the terrain and no where you are baiting him while keeping him in the center. Just run into his left most of the time and be ready to jump left at any moment, turn up the sound and listen for the kanji as missing it on his skin was the big problem for me after the terrain. The malcontent ring also makes phase 3 a joke, not sure if it does anything but I also used Devine confetti in phase 2 and popped ATK suger in phase 3 with the ring.Â
Wait, Malcontent whistle stuns him? In that case I should have him beat in a couple of tries tomorrow morning!