Labyrinth of Touhou 2 - Epiphany Ame-no-Murakumo
5This boss took a LONG time to prepare for. First I needed a couple tanks who could survive a few direct hits from True Greatsword. Then I needed a way to kill both of the adds before they used an aoe attack most of my party is incapable of surviving.
Do not hit the main sword while adds are up or it will counter you with a VERY hard hitting SPI/DRK counter attack. Every time it resummons adds it adds an additional turn before it can resummon more of them. First you need to focus entirely on killing them to drive this counter up. Once the counter is high enough you can finally start to bring down the sword's HP pool. He still counters you with a fairly hard hitting basic attack.
Both arms will eventually use a party killer attack on you that is VERY hard to survive. One of these attacks even destroyed my tanks with one hit so don't let them live for too long. The right arm has some physical skills but it's most dangerous attack is True Greatsword of Calamity. It uses this VERY often so you need to plan to deal with it. The left arm has a number of magic aoe skills that will wear your party down rather quickly. It is notably weak to 4 different ailments including TRR and PAR but not debuffs. It will also use it's party killer a few turns sooner than the right arm will. Watch out for their damage output if the sword buffs their offense. The sword will generally make your life miserable with buffs, healing, and some unique effect moves. Watch out for the one that shuffles your party around and the one that reduces your HP to 1! You can easily have deaths or even wipe on the spot! When you are about to kill the sword make sure you have SOMEBODY in your frontline that still has TP left. The sword has moves that reduce it to 0.
You need to use FIR or DRK physical attacks on the left arm and you need to use NTR or SPI magic attacks on the right arm. Defense/Mind ignoring attacks will also work. The sword itself is neutral to everything but SPI and DRK. TRR also works on the sword. The TRR core is notably good here for killing the left arm and also damaging the sword despite it resisting DRK attacks. Just make sure not to accidently damage the sword while any add is still alive.
Once both adds are down you don't really need a dedicated tank so feel free to have 4 damage dealers and pump out the damage! Just watch out for counter damage and have a way to heal off the damage. It hits rather hard. Make sure to keep your key damage dealers alive without too much max hp damage from the aoe DRK attack that reduces it. Also make sure you never leave an add alive for too long. Especially the left arm.