PARTY:
(with the LV before beating the Boss, I took the prints after playing a little more)

1 - Sumireko - LV86 - Full Elemental Damage

- I was trying to level up my Sumireko to at least LV90 before the fight, but I got bored and stopped at LV86. It worked in the end :)

- Just dump all your points in MAG - VIT (Both to 99) and the rest in INT.

- I used a moveset with every single element (to cover that disgusting "Paradise Lost" skill), "Debilitating Aura" (the boss WILL target your Sumireko non-stop) and "HP-MP Spring".

- For equipments... I just used everything that gave Sumireko the most protection and magic damage.






















2 - Shinki - LV99 - Full Elemental Damage

- You can Hijack her while you navigate around Pandemonium (never again). She'll be LV97, so its very easy to LV99.

- I used the exact same moveset as Sumireko. they both will hit +-1k per turn, so you will (probably) finish the fight before running out of MP.












3 - Sariel - LV94 - Full Healer

- You can ALSO Hijack her while suffering in Pandemonium (never again). I just used her because she was already at a high level (my Sleepers were around LV79 ~ 80) and with high VIT.

- I used 1 party healing spell, 1 status condition healing spell (I hate Paralyzis) and 1 revive spell (didn't had to use it), "Praying Stance" to keep healing everyone (without using lots of MP) and allowing me to keep using "Defend" and getting SP (VERY important), 2 buff skills that I never had to use and "HP-MP Spring".












4 - Hecatia LV66 - Full "HEAVEN AND HELL"

- I literally just Hijacked her, put some skills, and sacrificed some sleepers to up her LV a little bit. I WANTED to get Hecatia to at least LV80, but I got bored and had no money, so I just left her at LV66, and well... It worked!

- "Heaven and Hell" is all you'll need... And sometimes a status condition healing spell (I HATE PARALYZIS)

- Your Hecatia NEEDS to be the last one to make a move (in order to effectively counter "Paradise Lost")

TO DO LIST:

1 - Get only your strongest potions (Miyoi Special)

2 - Turn ON the "Youkai Grimoire: Sting"

3 - Know how to count to 6

4 - Use 2 "Booster" to get your SP at MAX

That's it.










































:)










If you are having trouble and ABSOLUTELY no luck with the Boss AI, maybe its time to turn On the "Youkai Grimoire: Easy"

This is the "fun" part

FIRST TURN:

In the first turn of the battle, the Boss will do 3 moves, 2 of them are probably going to be attacks (that 99,9% WILL get you paralyzed) and the last one is going to be "Paradise Lost"...

Holy ZUN...

"Paradise Lost" is unfair. This skill will make the Boss get a random weakness (ALL the other elements are going to heal the Boss), get ALL buffs to MAX and debuff YOUR PARTY to MAX. You. Will. Die.

In order to not die, You will "Defend" with Sumireko and Shinki, use "Praying Stance" with Sariel and use "Heaven and Hell". Pray to not get hit in a weakness within the 2 attacks before the "Paradise Lost" activation, because this will make you not be able to activate "Heaven and Hell", and you will die.

SECOND TURN AND ONWARD:

So you managed to use "Heaven and Hell" and swap the buffs & debuffs with the Boss! Great!

Now the countdown beggins.

Every 6 turns, the Boss will use "Paradise Lost" to change its weakness and debuff you. So you NEED to count, and EVERY 6th turn use "Heaven and Hell" to save you (Hecatia being low LV makes her be the last to take action, ensuring that you will always use it after "Paradise Lost" and getting all the buffs for your party, but with the risk of having low HP)

In order to fill the requirements to use "Heaven and Hell" every 6th turn, you'll need to keep hitting the Boss weakness with Sumireko/Shinki, and "Defend" with Sariel/Hecatia. Doing this will make you have a full SP bar by the 5th turn. If you need, you can use Sariel skills to Heal/Clear your Party instead of "Defend", you'll still be able to reach the SP requirement (If not, you can use a "Booster" in turn 4/5 to MAX you SP)

WIN OR LOOSE:

Well... that's the strategy!

Keep hitting the Boss weakness (To do around 2k of damage per turn thanks to the "Sting" book), "Defend" and Heal when needed and use "Heaven and Hell" skill every 6th turn.

"Heaven and Hell" and "Miyoi Special" will give you all the buffs you need. So just keep an eye on healing and SP gain.

Some stuff to remember:

The Boss can ruin this strategy by:

- Paralyzing Hecatia in the 6th turn

- Hitting a Sleeper weakness in the 6th turn

- Killing your Hecatia before the 6th turn

- And probably some other things that didn't happened in my tries.

You can ruin this strategy by:

- Forgetting what turn is (I had to restart it 4 times, because i forgot to count the turns after some time. "Paradise Lost" made sure to punish me for this)

Edit:

Just tried again, and I got to beat the Boss 3 times in a row! You just need a little luck at the start of the battle, but if you get the first "Heaven and Hell" to work, you basically won the battle (as long as you don't forget to count the turns).

*You can force "Heaven and Hell" to work by making your Sumireko/Sariel use a "Booster", even if the Boss hits you in a weakness, the "Booster" will cover the SP in the end, allowing Hecatia to do the funny skill.



Aaaaaand... That's it!

Decided to make this guide to help players (like me) who are lazy and dont want to farm new sleepers to defeat this amazing Boss and get that funny little achievment.

Hope its readable :)

Video on how to do it: