That's the fight with Goetia if I can recall correctly he does the NP 1st turn, then has 3 turns that negates NP damage to him.
If I can recall correctly, this is how my fight went with him (Mainly because I refused to use quartz and kept waiting for my command seal to recover) so I tried at least 3 times.
What I did was, 1st round, I have the frontline row have some people with high normal attacks. The back row has some Heracles support with the Guts 3 times CE (the fight will be easier with 2 Heracles) and some one who can fill the NP gauge or raise Heracles attack or Buster attack. try to have someone who has target focus so Goetia can focus his attacks on it, when the 3 turns go out, smash him with Herc NP.
So, the breakdown of my fight was, 1st turn, my front row was made with Seibah, Arash, Cu Cuhlain (lancer), backrow was Support Heracles, Santa Seibah, Elly Brave. Everyone on my team was wearing a increase NP damage CE. My mystic code was the battle mystic code.
1st. I let the front row die.
2nd turn. Goetia focus on killing Heracles, but Heracles has 3 times guts, so 2 are left. It was a stroke of luck that the card draw was 3 Heracles buster, so, I used his increased attack, dealt around 120k damage on him.
3rd turn. He spread out his attack, so everyone still survive, just dealt normal attack on him.
4th turn. The same
5th turn. I let everyone die to his NP. but at least his guard against NP damage is gone. used command seal to revive
6th turn. I let him have it, overall NP damage was 300k. since Arash always an heroed on NP, Herc, came out, and I swapped it with Elly Brave
7th turn. Elly Brave NP. dealt around 120k (because of bond damage bonus too).
then after that, it became a war of attrition until the last guy, Heracles came up, then I used NP, and smashed that ass.
My overall tip, for me, the real fight happened after he wipes the party 1st time, since he has his null NP damage for 3 turns, try real hard to let him fire his NP before your party wipe. the support Full Bond Heracles with his 3x Guts CE is my MVP here (thank you **************)
Ganbatte!!