No protagonist recruits: How three units defeated enhanced level-99 BalorMajor spoilers
Even three level-99 units lost the first attempt. Giving Eshmel the magic weapon and critical-hit healing, then breaking gates and attacking in the same turn, secured the clear.
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Loadouts for the no-protagonist challenge
Recruit none of the four heroes and enter the Promised One’s story directly. Leave the Underworld gates around the world intact to challenge enhanced level-99 Balor. The three deployed units are 
Eshmel, 
Troy, and 
Hong Hua, all trained to level 99 with S+ proficiencies. Stat boosters are held in reserve unless the fight proves impossible without them.
Eshmel uses 
Great Knight, with both mounted and armored types, allowing armored movement and 
Healing Armor. At 54 Magic, Healing Armor has a 54% chance to restore half the damage dealt as HP, letting him heal while fighting. Troy uses 
The Godhand and Hong Hua uses 
The Avatar. Both originally rely on 
Sacred Gem for healing on critical hits.
Hong Hua’s Resistance also works with damage-reduction abilities, and magic weapons use her Magic. All three visit 
Castle Knight for damage reduction. With so few units, everyone needs as much self-sufficiency as possible.
The first attempt failed from poor healing and blocked paths
Troy’s Critical is the first problem exposed. The plan was to heal through critical hits, but against the actual enemies her chance is only a few percent, or even 0. Without a critical, she gets no healing, forcing Hong Hua to spend actions healing her. With only three characters, that means fewer actions both to clear enemies and break gates.
Healing Armor helps Eshmel stay alive, and multi-hit sword Combat Arts deal damage, but flying enemies constantly block his path. With a Range-1 sword equipped, he cannot counter enemies attacking from two tiles away. Without clearing them, he cannot reach the gate. The weapons were also left unrepaired. 
Levin Sword and the swords used for Combat Arts run out of durability in succession, and the attempt ends in defeat.
Reassign healing equipment and Warp the main attacker first
Using the reserved stat boosters raises Eshmel’s total stats to 523.
| Eshmel’s two attempts | Total stats |
|---|---|
| First attempt | 477 |
| After stat boosters | 523 |
Both Levin Sword and Sacred Gem go to him, while Troy switches to Victory Gem for healing on kills. Since her actual Critical is low, let her recover through kills she can achieve.
Open by warping Eshmel near the body, then break a gate so the barrier-breaking turn can lead directly into attacks. The blocking armored enemy has high Defense but low Resistance; a Levin Sword clears the previously difficult path in one hit. Dismount before fighting enemies with effective weapons rather than taking the weakness for free.
Use a five-hit sword Combat Art against the main body. More hits per action also mean more chances to crit. Still, Hong Hua and Troy need healing available. Do not trade survival next round for one more broken gate by relying on an uncertain critical hit.
Attack the main body in the same turn a gate breaks
Blocked paths remain the biggest problem later. If fliers stay alive, the main attacker cannot move and the gate breakers cannot approach. Pause gate breaking for a round and focus on clearing obstacles. That is better than opening the barrier when nobody can attack.
The boss powers up after losing HP bars. Its final section has more HP and takes less damage, so do not estimate from the first phase. Hong Hua and Troy must stay alive first, taking turns clearing paths and healing, then looking for where gates appear.
The final sequence uses Rewind to adjust the order. Break a gate with long-range magic first, then move the healer into a position that covers teammates, and have Eshmel attack that same turn. Next round, kill the enemy blocking the way first. Hong Hua advances until 
Bolting just reaches the gate. Once it breaks, Eshmel uses another multi-hit sword Combat Art, with a critical among its hits finishing the remaining HP.
Divide leveling and money tasks before the finale
I used Normal/Classic, keeping experience after failure and retrying to max levels and skills. Train White Magic in the arena first so all three learn healing. Heal gave 10 experience per cast here, faster than the 1 experience per fight at high levels. Proficiency still needs repeated combat. Even so, the save already showed over eighty hours, with resets adding more.
This route starts with an unexplored world map. Troy and Hong Hua must split up to explore, so both need training. You cannot develop only the Promised One. Money also starts at zero. With combat strength stretched too thin, even earning money along the way becomes difficult, making later equipment harder to obtain.
For another attempt, plan where to level, where to earn money, and who will open the map. Fully repair weapons before the final battle, and confirm that all three can handle their own healing and gate-breaking duties. Level 99 solves the stat problem; winning still depends on dividing actions well.