Did the entry for the
Last Word Charge behavior which is actually unconfirmed on the JP wiki, I am sorry I couldn't do the one for Shield behavior but that one is harder to understand, and test to be fair as Shield behavior is pretty random varying from shield to shield at times. Here's the rest of the old docs by the way:
http://pastebin.com/u/cjd2524
Nitori Lv.75 / pre-expansion equipment (guess the combination):

Takes a real while at that level and could be done with a little I guess, it's a shame there is a unique LW, and not selectable LW types (like Support, Offensive, etc.) because it really shows how Last Word gimps certain characters, Youmu is barely able to stay alive nevermind attack under the same circumstances (that thing can deal 8k damage per turn). Stances would have been nice to further extend formation variation, similar to three sisters Battle Stance or Youmu's, since freefight is fixed (SPD + LW+1).
Also the decision of having the LED Mirage + Basch pair only spawning at end of the of the Endurance Dungeon, the ultimate Sakuya battle ruined by bad placement, though the mistake here is that there is no way to re-enter from the exit (and with no custom arena), I would be happy if there was a way to hack enemy encounters for testing purposes.
Final Boss (from what I remember):
PHASE 1: these ones can be soloed with Youmu if one would be ok with sacrificing the best gear, still fun to try.
Both have 50% Exorcism, making total % Divine Barrier half as effective. After the 12th turn Sekigyumon will be able to use Comet and Seigyumon Hyper Bomb, remember this skills has 25 Exorcism, and Comet has 50 Exorcism which stacks as well, this last nulls Divine Barrier completely.
The most dangerous skill in this battle is Seigyumon's Vacuum Wave, since it can deal 4 digit damage to a character with no SLA Resistance or Physical Barrier, however just like Hyper Bomb and Comet it will be a added to the moveset after the 12th turn (this is not what I remember), unlike their two signature attacks this one is used much earlier and relentlessly (Hyper Bomb is STK Physical, Vacuum Wave is SLA Physical and ignores all DEF, both relatively low Accuracy).
It is best to prioritize Seigyumon if anyone in the party is able to Debuff MATK, while Hyper Bomb damage can be halved in many ways unlike Comet, both Phase 1 Bosses have 95% PATK Down and ALL Down Resistance, but no MATK Down Resistance, or ACC Down Resistance (only Lv Resistance / 18% Variety), both can be easily inflicted with either, reducing Comet damage dealt, or Vacuum Wave and Hyper Bomb Hit Success (remember minimum Hit % is 5% regardless of ACC, so is not secure like MATK Down).
If by any chance Sakuya is picked as Leader (or not, but more likely to be targeted as leader), and she gets attacked and gains her Last Word on the first Turn and there are buffers on the party, Byakuren with her Perfect Resist specially, as both bosses they are likely to end wasting multiple turns using Vortex if Perfect Resist is present, both will be gone before they even a chance to use Vacuum Wave, much before they get a chance to use Hyper Bomb or Comet.
PHASE 2:The Giant Fish Face has two signature attacks, the most annoying being Indigestion (was that called?), which drains 90% of Current HP and ignores defense and almost always succeeds, this make it soloing almost impossible, even with perfect Regen. The second being Abyss Wind, watch out if using a speed halving formation like Master of All, as it has a high chance of inflicting Curse and cause self-death if the player decided to go on an all out attack in the same turn.
Any character capable of inflicting Poison (or variations) will easily help getting rid of the Giant Fish Face while leaving alive the Mirrors (Sanae is made for this battle), since the battle will go on as long as at least one mirror is present one can take the needed time to heal, and buff prior to the following battle, the Mirrors only powerful skill is Hyper Destruction Beam, which increases damage as it hits more targets, from the top part of the screen to the lower (it is not too powerful anyways).
If there is any party member with the ability to buff this is the perfect time to before Phase 3, again specially Sanae, as only Phase 1 bosses have Dispel capabilities one can easily make room to raise all party HP beyond 1000 HP to secure Phase 3, and if Mokou's is in the party even get Perfect Regen. Even if no one is able to buff one can wait to see if Last Word activates for use in Phase 3.
PHASE 3:Has 3 signature attacks with Emperor's Pandemonium being the most dangerous, it's VOI Physical based and as such can be Deflected, Alice and Youmu's are likely to, Satori's 1-Star Commander Spell can help a lot if properly used, specially in conjunction with Alice's Little Legion. While it is not mentioned anywhere I think it powers with each missing Resentment meaning it does around 999 damage only when the 4 Elementals are down and is nowhere as powerful when done randomly at will.
Satori's Shield Wall can reduce Emperor's Pandemonium damage to 250 or less, however her SPD better not be halved by a formation penalty, Shield Wall casting SPD is Satori's SPD x10, while Pandemonium's is Boss' SPD x3, with no resentments SPD = 400 -> Skill SPD 400 x 3 = 1200 SPD, good luck if satori has less than 120 SPD due to formation.
Sakuya's Time Stop (if at Level 99) can be used easily to land hits and hold back for one turn the dual attacks.
Alternatively Cirno is made for this battle but I never got to test her, basically the boss has 0% Freeze Resistance when all the Resentments are down, which is a 100% guaranteed freeze, meaning Cirno uses Ice Counter takes the damage of only the first attacks and interrupts the second one. However she has to survive the first one, while only Pandemonium is worth interrupting I think it can also be the first of the two attacks.
Sakuya could as well inflict freeze, but Cirno's Counter is used to circumvent the SPD requirement, she needs to exceed SPD 1200, supposing Aya isn't in the party or as a Leader, the only possible way to do is by buffing her SPD with Sanae or using Sonic Stream which sounds super risky for the other Phases, and since Sakuya can manipulate time by herself is a really inefficient workaround.
I always found a single party to be the best, due to the lack of alternative tiers for equipment, this is really notable in the pre-expansion final boss (MYS Resistance anyone?), but even here with all the extra expansion equipment, it ends coming short due to the new attacks and extra party members. The three phases can be taken down around 20th turns likely if not even less, it can really depend on Last Word Activation.