Defeating the emperor on a single-route run: hold the healing platform, clear reinforcements, then break shieldsMajor spoilers
Use the lower-left platform and narrow entrance to block golems and let enemies approach. Keep the protagonist alive and clear reinforcements before pressuring the boss again.
Original video: Defeating the Dagdan Emperor on a single-route run | Fire Emblem: Fortune's Weave; Bilibili creator Koudaimi ag; https://www.bilibili.com/video/BV19VeM6NEZf/
Hold the healing platform entrance to block golems
Check the upper-right map first. A healing platform lies to the left. Pull the team toward the lower left and use the entrance and tiles to block access, making it hard for golems to approach.
Do not chase them. Counter the soldiers who can reach you and leave inaccessible golems alone for now. Keep 
Hong Hua outside the boss’s attack range in particular, since she can easily die in one hit. Others may not survive two attacks either. Check who will be targeted before settling into position.
Clear miasma, then handle reinforcements in groups
Remove one boss health bar, wait for reinforcements, then retreat to the platform. Do not chase the boss while soldiers rush in from the sides. Clear this wave before returning to the boss.
Miasma around the boss prevents follow-ups, so even high Speed gives only one round of attacks. Clear it with Blaze Arts before fast units engage, preserving their second hit.
If terrain colors are busy, display the grid and darken enemy attack ranges so dangerous tiles are visible. Keep watching the upper-right map rather than only combat animations.
Focus enemies carrying gauntlets first. Even if enemies approach separately, do not split units off to chase. Stay within your existing firepower and let them enter it.
Use platform healing to preserve the protagonist
Eshmel must survive. If another ally falls after a mistake, you can try Rewind. The protagonist’s survival must be secured in advance.
The healing platform also supports Blaze Arts. Their use costs HP, which you can gradually restore on the platform while building the required state. If enemies cannot reach you yet, there is no need to leave safety.
Focus shields, then give lower-level units experience
Concentrate attacks on the appropriate shield section, then follow up after breaking it. Keep nearby golems blocked. Do not reopen the entrance just to break a shield.
Remaining soldiers can also provide experience. A high-level unit already at level 47 need not take the final blow. Let lower-level allies kill them and grow while clearing the battle.
Restore enough HP before using Blaze
When preparing the final attack, I found an ability unavailable because HP was too low. I stayed on the platform to heal instead of rushing.
The enemy’s Attack is high. If current HP is insufficient, wait another turn. Prepare Soulflame, distance, and HP before charging. With the position secured, waiting is better than losing the protagonist to rush one attack.
