There is only bad end for me, man.. that seriously not the end she deserve, but it still beautiful.. the world is just too harsh to our cute little Polca.. i cried, i just want her to be happy man., i really hate you Akai Mato for giving me such roller coaster feels..
Also the secret
Here is how I did it and my party
Polca - Dedicated healer and buffer. Use her to heal on every single turn and if you somehow don't need to heal use the attack boosting demon skill (Loki Roots I think it's called).
Diana - Use "Kick-Ass" every single turn focused on one enemy to make sure they are always on double defense down status. Can also serve as a backup healer when you don't need to defense down with "First Aid" and "Emergency Treatment" if somebody gets paralyzed. She is also essential for removing "Do-or-Die" status from the commander once they activate it.
Lily - You main damage dealer. Equip her with the Crystalized abyss Sword (found in the EX dungeon from the Sage's place) and the Onion Cape. Use the "pleasure" skill, attack until the pleasure skill is gone, and use the pleasure skill again. Focus all your attacks on the same enemy that Diana is debuffing until they are dead.
Najezta - He is here to mainly use "Fish Scale Formation" to give Lily a much higher chance at landing crits with her attacks. Also when he is at 100TP use his special "Imperial-Style Tenfold Sword" every single time as this has like a 90% chance at making the entire party of enemies slip causing them to miss a turn. He can also serve as the emergency backup healer if Polca is incapacitated for some reason.
I highly recommend taking out the Mage first as he deals the most damage and then the Priest as he is one the that casts that annoying spell that heals them for 45,000 HP every turn. Use the above strategy with some ad-libbing if things get extra hairy and you should win pretty easily. Honestly, once the mage is gone the fight is a formality since his damage is the most threatening thing which is why you should focus on him first. All characters were at level 99 for me. I actually haven't tried the fight after this one yet though but should do that soon.