Here you go, jaxter0987. You can make a change in anything as you see fit. This is the first time I have written a strategy after all. Thanks in advance!
Desire-Eating Demon
Time for a flat-out damge race battle. The Desire-Eating Demon's attacks focus mainly on status effects and debuff. Your party should be protected against PSN PAR SIL HVY TRR and DBF, particularly PAR SIL HVY DBF. Those attacks do little damage.
The main problem of this fight, however, is that during its 4th turn. The Desire-Eating Demon will use its most fearsome attack Empty Mouth That Swallow Sinners. It is a single-target Dark attack that deals around 1 MILLION damage and inflict DTH, regardless of resistances. What's worse is that it doesn't always target the leftmost slot so you should consider switching your important character back in when the DTH attack is coming up. After it is used the first time, The Desire Demon will alternate between its normal attacks and DTH attack. Needless to say, you have to defeat it quickly before your entire party is decimated one by one. The boss has very high HP and is rather fast so this will be a long and difficult battle.
The Desire-Eating Demon is weak against CLD and NTR but highly resistant to MYS, SPI, DRK and PHY and neutral to FIR and WND. So Nitori, Nazrin, Yuugi, Suika, Kanako, Suwako, Yuuka (or anyone with a Monk Subclass) is your great damage dealer here.
It is weak against SIL and SHK and resist Debuff so prepare your characters as you see fit. Inflicting SIL can help lowering its MND. Inflicting SPD debuff can also slow the boss down a bit. Its weakness to SHK should be exploited so bringing in Kasen, Reisen, Remilia, Flandre. Renko and Maribel. Orin and Kogasa are highly recommended in this battle. Kogasa can help SHK and deal Nature damage with her Karakasa Surprising Flash while Orin can SHK the boss reliably and continuously with her low-delay Cat's Walk. Renko can both inflict SIL and SHK on the boss.
Do note that most of the boss's attacks have a very low delay so its next turn will come faster. The DTH attack has the delay of 1000 so this is your greatest chance to switch in your attackers.
Also, I see on the wiki that The Demon weakness to CLD and NTR is black instead of red so please change that. Those have different meaning in this game. (Red = Weak, Black = Very weak)
And which floor do you need overview? I have played the game several times so I might help with that if I have some free time.