Sheesh. The Type-0 D??? was rougher than I was expecting, but finally got a mastery clear in 56.37.
Rem (LM1+LM2): R5 Holyja, R2 Hastega, MM (BSSB/OSB), double holy boost, fire/earth resist
Sice (LM1+LM2):, R3 Memento MOri, R4 Dire Heal, Dark Ability DMG+ (BSSB), double dark boost, fire/earth resist
King (LM1+LM2):, R4 Tempest Snipe, R3 Spark Offering, Scholar's Boon (USB), double lightning boost, fire/earth resist
Deuce (LM1+LM2): R3 Shellga, R4 Curada, Gathering Storm (BSSB/USB1), fire/wind resist
Machina (LM1+LM2): R4 Tremor Assault, R4 Blastspell Strike, Swd DMG+ (USB), double earth boost,earth/holy resist
RW: Realm chain
Magicite: Lakshmi (L20 MND Boon/10 Dampen Dark), Famfrit (L8 Blade Ward/L8 HP Boon), Phoenix (L8 Spell Ward/L8 Blade Ward), Madeen x2 (L20 ATK + L20 Mag Boon, L8 HP Boon + L10 Fast Cast)
I can't even list a decent turn order since it's rather chaotic and I was partially playing by ear. But roughly:
Rem: Hastega -> BSSB -> spam Holyja, time Hastega after P1 Dispel, OSB to help get past Phase 3 faster, refresh BSSB, more Holyja spam, OSBs at the end.
Sice: MM -> Dire Heal spam. In my winning ruin, I actually don't use her BSSB until late in the fight, after the Dispel in P4 that I can't skip. I ran out of hones with her and had to resort to using her BSSB CMD1 at the end.
King: Offering, chain, offering x3, magicite, USB, Tempest Snipe, drop USB near end of chain, refresh chain, Tempest Snipe, USB, magicite, then whatever to finish.
Deuce: Shellga, Curada x4, BSSB, Curada, Shellga after P2 Dispel, drop USB1 before P3 Incubus Ultima if party not near full HP, otherwise wait until after P3 T3 Death to use USB1, BSSB CMD1 to spot heal anyone too low, time Shellga after P4 Dispel, otherwise Curada, USB1 before P5 T2 INcubus Ultima, Curada aimed at Rem or Machina
Machina: Blastspell Strike x3, USB, Tremor Assault spam, refresh chain, Tremor Assault spam, USB to help skip Phase 3, Tremor Assault spam, USB to finish.
These turns aren't remotely set in stone, especially not near the end. Who refreshed chain depended on who couldn't fit in another damaging action before chain ran out. Speaking of which, I ran out of third chain around 50 seconds and had to grind out the last 150,000 or so HP without. I think I won after P5 T8 Ultimate Quake, before Incubus Ultima (though I had fired off one last Deuce USB so I would have survived it), so cutting it rather close.
I could probably speed this up by swapping Ace (BSSB/OSB) for Sice, since she not only ran out of hones, she was barely doing damage throughout. But having beaten this, I'm in no hurry to revisit it again without better gear. I'm good for now.