Actually, I found the Berserk Charge ability more of a detriment than a help in this fight.....
When he combo's on the ground, jump, air dodge, then start air comboing him, Finisher Plus helps too
Issen, as has already been mentioned, use reaction command, though it sucks being mid-air when he does it.....
Heartless Angel, either go and get him asap, or ready your elixirs so you throw one just before you get hit, so as soon as you go down, you go straight back up.
Shadow Flare, just use air combos to reflect them all
The Fire Pillar move thing, keep away, time it just right so the "pull" from them can draw you in just as they fade to get in another combo
And remember, in an onslaught against him, you can only do 2 finishing moves against him before he teleports, so don't hammer the X button too much