Do you want my save file for this build? Shoot me a message on the talk page here and I'll hand it over. I also have a completed legit, high BR, normal mode save file right at the Sacred Lands (without At Hatred's End finished).
After many trials and even more errors, I have finally achieved something close to what I want.
- Must be in hard mode.
- Finished all quests to get The True Conqueror.
- Finished At Hatred's End. Not doing it gimps the Conqueror from using Abyssal Seal.
- Have not killed any DLC bosses (apart from the ones required to be able to see Demigod).
- Party has maxed stats. This means 255 strength, etc, 9999 unit hp, +99 AP per move, 999 max AP.
- Party must have maxed arts. All possible arts must be at max. (Peerless or Swift depending on equipment of course.) All union leaders must have each arcana learned, to level 5.
- Every single weapon or shield must be at +9 in terms of strengthening.
- Each unit must have all the arts it possible could have under its arsenal. When a unit asks Rush if he/she should try a new skill, the answer must be YES. You can always disable bad arts/skills later.
- The equipment of each unit must fit my requirements:
- They must all allow for a weapon art (in some cases, a leader's unique art will do if no satisfactory alternatives exist).
- Out of all 18 units that are assigned, for each possible combat art there must be at least one unit able to perform the art under normal circumstance (dual wield accounting for power grip or one-handed arts do NOT count). This means there must be a unit that wields a katana one-handed by default and can use Snowfall and another unit that dual wields katanas and can use Spring Squall.
- In addition to weapon variety, there must be a shield for each size. (Small, medium, large, extra large)
- Variety. I don't want 500 Heaven's Doors.
- ...But also prowess in battle. This setup needs to defeat The White Conqueror on x10 HP or more. More HP is a liability because this means there are more chances for him to kill all units with a lucky streak of AoEs. Unfortunately, his War God is physical yet his Fatal Eclipse is mystic. The units must survive an onslaught of these two types of attacks over and over and over.
- I give myself the liberty to manually equip each unit as I see fit.
- Party must have at least one of each race. (An easily met requirement.)
- Party must have "ideal" formations. This includes where each unit is placed in each formation.
- One union must be able to force trigger Crimson Flare V.
- Accessories must be "ideal".
- Classes for each unit must be "ideal".
- Cannot have equipment that cannot be obtained. For example: Having two Nightbloom Virtutis is an impossibility no matter how many New Game+ you do. One per playthrough because it is a drop that cannot be made at a workshop and weapons do not carry over to the next playthrough.
- Using trainers is OK.
That is a long list of requirements and some requirements conflict partially with another requirement. Finding the right balance is key. For example, the idea of having unique weapons that come with each member of the Seven is quite enticing but it's actually a big problem. While they all typically end up being at 255 attack if not close to it after +9 strengthening, they do NOT allow for a weapon art. I can't have all of them be party leaders. And not all of the unique arts are even GOOD; Snievan's Phantom Pain is low damage, and Milton's Iron Will is a joke. I think Iron Will should have affected all unions to balance it out. I did let Hannah become party leader to enable the guaranteed Twin Snowpetal at the start of each encounter. However, this has a major drawback in that I am giving up two units that could do weapon arts in exchange for a guaranteed, one-time, Twin Snowpetal. Note that the Nightbloom Mist/Royale itself does not allow for Snowpetal weapon art.
My original attempts were very sloppy. Failures include: Adding Duke of Ghor to the party via trainer without doing his quest - making the quest impossible to complete, thus blocking The True Conqueror. I had to totally start from scratch. Another time I saved over my save before I bought Demigod, breaking one of my major requirements. Starting from scratch. What I later found out was that in these marathon challenges with bosses having x10, x20 hp, it's really about union defense, not attack. War God would wipe out all unions at max HP. That's just not going to work when my survival is dependent on chance. On the other hand, I can't have everybody equip shields because that would violate one of my other requirements, which is variety. In terms of accessories, this is another problem. I decided to go with Doom Chain whenever possible for the crazy mystic and physical defense, but that leaves me vulnerable to status effects. Animalcule will totally cripple everybody and some unions rely on mystic arts for healing. That means each union needs to have one person with an Idol Amulet for its Debuff -5 effect, negating negative status effects. That goes hand-in-hand with avoiding AoEs like arcana: The less unions I have, the less Doom Chain slots need to be used up for Idol Amulets. However, the less unions I have, the more units each union must have to fit all 18 units, meaning I take more damage from AoEs relative to my total Hp across all unions. (This is because no matter what configuration I use, each union will always have 9999hp; 3 unions of 5 units is 9999hp each, but 5 unions of 3 units is still 9999hp. As long as I have 18 units on the battlefield, the amount of damage taken per person is the same regardless of the amount of unions I make to put these 18 units in.) It is probably ideal if the unit that is using Idol Amulet for the union is the one with the highest overall defense. This is because a unit with less defense gets a higher amount of damage when attacked; that means reducing say, 15% of that damage turns out to be a bigger number. Regarding shields: In general, I want a shield that specializes in evading the type of attack the weapon is not good at defending. I'm trying to prevent sudden death, I need a good balance of defense and/or evasion for both physical and mystic attacks. So the weak spot of a shielding axe would be mystic defense, so a 1H unit would use a shield that protects against mystic arts. I cannot have a unit with one-handed default attacks but not have a shield equipped, that is bad.
I've decided to go with Legendary Guardian for all the units when possible. The Physical +5 and Mystic +4 defense bonuses are more valuable than Combat Arts +5. Again, I am being very defense oriented. Damage is nice, but useless if you get sudden death from an unlucky turn on Hard Mode. I'd rather have lower attacking power but be able to survive anything anybody throws my way. However, I am using the Trident formation because it allows for my build to work and to prevent any penalties. The penalties are for position 4 and 5 on Trident, and having only 3 units per Trident union allows for only the benefits and none of the negatives. I didn't choose the defensive formations because the formations are full of caveats and weird penalties that are hard to use correctly. This setup is more than enough to kill The Lost in five moves. It took only two moves on my first try, and The Lost was unable to KO a single union due to my high defense against everything.
The result of my formations is that the the Trident unions are all Trident I instead of Trident III. In my mind there is no point in Trident II because both Trident II and III require 5 party members, it's just a different number of Sovanis for the most part. With III there is an extra 5% CA damage effect on top of an extra 10% attack boost (the latter of which only applies to units 1 to 3). On the other hand, the magic defense for units 4 and 5 in Trident is very low and is a liability in many boss fights. The attack boost is of less use to units with weapon attack closer to 255, and that must be taken into account with unit placement. Zephyr has tested the attack bonus of formations with a weapon of 255 attack and found that it does not help break the attack cap. 
And so, if I want variety by having a union that can do all arcanas I will need a 5 man union.
Arcana Union + Melee + Melee + Melee + Melee
5 + 4 + 3 + 3 + 3 = 18
5 + 5 + 3 + 3 + 2 = 18
5 + 5 + 5 + 2 + 1 = 18
The first setup is to have the most balanced number of units per union possible. The benefit to that is each union will tend to take a more similar amount of damage per arcana. On the other hand, bunching up the unions to the extremes like the third option would improve damage because I could have two Trident IIIs with two unions of 5.
Current setup: [Units listed by each slot for a formation. So first person listed is in slot 1, second is at slot 2, etc etc. Also, I list the wield style to make sure it checks out for my wield style requirement. Asterisk means the person is a designated medic of the union. Special Arts column only shows the arts I plan to enable.]
|Name||Class/Union Formation||Weapon Slot||Weapon Slot||Accessory||Accessory||Wield Style||Special Art|
|Rush*||Legendary Guardian||Shielding Hawkwind||Shielding Hawkwind||Idol Amulet||Doom Chain||DW Axes||Omnistrike, Hawkarang, Arcanas|
|Emmy*||Legendary Guardian||Shielding Bluesteel||Shielding Bluesteel||Doom Chain||Doom Chain||DW Swords||Cerulean Rain|
|Young||Legendary Guardian||Shielding Highbrand||Doom Chain||Doom Chain||PG Sword||Holy Win|
|David*||Legendary Guardian||Shielding Bluesteel||Superlative Targe||Doom Chain||Doom Chain||1H Sword||Gae Bolg, Ex Machina, Cerulean Rain, Arcanas|
|Allan||Legendary Guardian||Oriax Dominus||Doom Chain||Doom Chain||DW Sovani||Holy Win|
|Torgal||Legendary Guardian||Halphas Dominus||Halphas Dominus||Doom Chain||Doom Chain||QW Sovani||Hawkarang|
|Glenys*||Legendary Guardian||Shielding Hawkwind||Shield of the Vanquisher||Idol Amulet||Doom Chain||1H Axe||Hawkarang|
|Duke of Ghor||Legendary Guardian||Bilqis Virtutis||Doom Chain||Doom Chain||PG Axe||Bel'kwinith's Fury, Arcanas|
|Baulson*||Legendary Guardian||Shielding Caduceus||Doom Chain||Doom Chain||2H Staff||Amphisbaena|
|Jager||Vagrant||Shielding Glaive||Idol Amulet||Doom Chain||2H Spear||Heaven's Door|
|Irina*||Legendary Guardian||Nightbloom Virtutis||Aura Tataraichi||Doom Chain||Doom Chain||DW Katanas||Omnistrike, Snowpetal, Arcanas, Force Trigger All Arcanas|
|Khrynia||Legendary Guardian||Superlative Demonblade||Doom Chain||?Witches' Seal?||PG Katana||Demonsblow, Dual Snowpetal|
|Pagus*||Legendary Guardian||Enchanted Morningstar||Doom Chain||Doom Chain||PG Mace||Hammer Toll|
|Ludope||Legendary Guardian||Enchanted Morningstar||Enchanted Morningstar||Idol Amulet||Doom Chain||DW Maces||Hammer Toll|
|Wyngale*||Legendary Guardian||Gaap Dominus||Gaap Dominus||Doom Chain||Doom Chain||QW PG Sovani||Swordflash|
|Hannah*||Legendary Guardian||Nightbloom Royal||Shielding Soulshield||Doom Chain||Doom Chain||1H Katana|
|Hinnah*||Legendary Guardian||Nightbloom Mist||Enchanted Soulshield||Doom Chain||Doom Chain||1H Katana||Twin Snowpetal|
|Bloctor||Legendary Guardian||Shielding Blackjack||Enchanted Nethershield||Idol Amulet||Doom Chain||1H Mace||Double Down|