Yeah okay I think that may be where I messed up, I've got a level 67 surt, and a 63 parvati as the personas that Im using the most everything else is probably too low leveled
I just used the decrease attack and defense on his main body,seemed to do the same to his arms but I could be wrong. When he preped his ultimate attack I would use the first round to either heal or attack his main body and guard on the second. Kind just rushed him once he started regening all his arms
(I did this on normal, not sure your difficulty) I had constantly used defence up and agility up on myself, and made sure Ryuji isn't in the active party because the sword reflects BOTH of his attacks. Mona as well so I can keep healing to delay the Final Guard skill as long as possible in the fight.
If you haven't beaten him yet, I second the notion of lowering the difficulty just for this fight. It won't affect the ending/any trophy earning anyways.