This guy is a pain (especially on 'hard' difficulty), this is because he has purple energy balls that act as a shield to protect him from physical attacks.
!! Kuji magic is the only thing that will work against him !!
** NOTE: Be sure to kill his minions for a Ki boost when you are running low or (like me) before you enter the battle create numerous Ginseng and health potions, so you can recharge and heal up quickly. **
The most efficient way to beat him is as follows:
When you first enter the battle hit him with the 'meteor storm' spell, this will destroy some of the purple energy balls and turn them red, meaning he is angry.
He will keep sending shadow balls out to turn animals into his Samurai warriors, on occasions he will also send one shadow ball directly at you after creating his samurai.
Attack the shadow ball and it will send it back to him, thus disorientating him for just enough time for you to send another 'Meteor Storm' spell in his direction. Again this will destroy some more of the purple energy balls surrounding him.
After you have done this he will start to chase you with the 'Ice Storm' spell. The best way to combat this is to keep running around the platform untill he stops and floats down just above the floor, this is the time to hit him with another 'Meteor Storm' spell to destroy a few more of his purple energy balls.
Keep casting the 'Meteor Storm' on him untill you destroy the majority of the purple energy balls.
This time he will come at you with the lightning spell (he will hit you 1-2 times, nothing you can do about that), just be ready to heal when you do get hit as it will kill you quickly).
As with his previous spell running is the only real solution to avoid being hit. An aid to this is the 'Slow Time' spell. Using this will slow him down and give you time to heal up when you get hit, and allow you to dodge most of the lightning.
Keep running untill he floats down to just above the floor again, then attack him with as many 'Meteor Storm' spells as you can fit in before he sends another shadow ball at you.
Deflect the shadow ball back to disorientate him again and finish him off with a final 'Meteor Storm'.
** Whenever you see him send a shadow ball at you ALWAYS attack it to deflect it back to disorientate him, giving you more time to cast more 'Meteor Storm' spells on him. **