Be aggressive. Hack away at him like his a grunt. If he deflects you, expect a counter and deflect that back to continue hacking at him like his a grunt.

If he does the jump attack, deflect it and look at him carefully to mikiri/jump his followup.

If he starts shouting for a flurry attack, spam your guard button (or learn the rhythm to deflect it) like your life depends on it. Or just sprint away, works just fine.

On his second form, everything's the same expect for his jump thrust attack that you can mikiri or the lightning attacks that you can do a reversal on (it's like a mid air mikiri, just jump, embrace it, then attack before you land)