The main body is immune to the 6 elements and weak to physical. So you'll need a physical-oriented team.
It has a front mouth that does support. It starts to use Elixir after 5 turns it was alive, so kill that first. It's weak to FIR and ETH and SLA
It also has another mouth that does some support attack, but if both mouths are dead, the main body will use Abyss Wind and revive both, so leave it alone.
The main body has 1500 PDEF, but has no natural resistance to variety and is also weak to DEF down.
Once you reach it to less than 33% HP, it will use a VOI fixed 999 damage on the whole party.
Ignores divine barriers, magic barriers(set chance to completely dodge magic), magic reflect, magic damage reduction, magic damage nullify, and reraise. How amazing.
You can still use Nitori's 3-bomb, or Super Duplex Barrier, or Starlight Barrier and the such.
Most simple way is to use Little Legion + Yata no Kagami.
Or you can kill the boss before it uses it.
As GuyYouMetOnline mentioned, using Reisen's special slayer is the best way.
I recommend Mokou too because you can kill the mouth with Fujiyama and Final Finger is less affected by PDEF.
I used Alice, Mokou, Reisen, Sanae, and Byakuren with Poison Shield for this fight.
And Mad Thunder actually does 3 hits 75% of the time. An exception when max-min=1.