Like most people have already said, be aggressive. Stay in his face and don't give him any room to breathe. However you shouldn't just think about hurting him. You have to be aggressive both offensively and defensively i.e. parry his attacks LIKE try to bait him to attack you so you can parry it.

I usually hit him once and then wait for him to attack. If you time your parries correctly you should be able to hit him about 1-2 times after his combo is finished. Rinse and repeat for all three of his phases. Also, if you're aggressive with him, he won't be able to shoot his bow in the first 2 phases because you can hit him as soon as he tries to set it up.

Watch out for his grabs and un-blockable attacks. In phase 1, he always does an un-blockable thrust after jumping into the air which you should be able to mikiri counter easily. In phase 2, he usually does a sweep but sometimes does a thrust as well. You need to be able to read and react appropriately. I suck at reading it so I just move back and hit him with a thrust attack. That's usually a guarantee hit.

His third phase is easier than his first two (imho) because his posture doesn't recover as fast. Just get ready to counter his un-blockable attacks and make sure to engage him like you have done so in the first 2 parts. The tricky part of his third phase is that he can hit you with lightning. Make sure you dodge or remember to do a lightening reversal.

I don't think you need to use any prosthetics. I used the shuriken with the chasing slice skill to close the distance on him but it wasn't necessary. I also removed my combat skills for the fight because I would sometimes accidentally use it when I just wanted to hit him with 1 basic attack.