Took a good 20 minutes on my victorious run. I managed to incur minimal penalties for once. My party for the battle...
Yuugi (89), Reimu (97), Yukari (81), Suwako (86), Eirin (81), Flandre (85), Kaguya (87), Marisa (90), Meiling (93), Ran (89), Patchouli (86), Suika (81)
It's worth noting that any videos I've seen of this fight have all had a minimum level of at least 10 more than me.
Anyway, bragging aside, that was intense. Eirin got killed off early, and then he killed off about one person a form due to Start of Heavenly Demise. I've learned to use the Fire phase as my healing and recovery time; the damage he does in that is actually really easily handleable, excluding the occasional Scarlet Gold Sword, and I can focus on restoring my buffs. Going into the final phase, all I had was Ran, Yukari, Yuugi, Suwako, Meiling, and Reimu left. I got lucky, and he didn't use World-Shaking Military Rule until a couple actions into his final phase. My final moments involved me swapping in Yuugi (After a buffed SoHD blew up Yukari, Suwako, and Ran) in a desperate attempt to get one more attack... and he acted a split second before and took out Yuugi with a Scarlet Gold Sword. This gave me precisely enough time to swap Reimu in, and I made a desperate attack with the only thing I had SP for: Evil Sealing Circle.
11k damage. "God damnit, I'm gonna lo--"
*VICTORY*
Also I had never ever used Suika before this. I don't know why, but she had never seemed to be doing any damage. Then I saw someone using Suika in a
Let's Play of the game and was very thuroughly surprised at how much damage she was actually doing. She really saved my ass; high powered NTR/WND moves were really important for me, since those were arguably the two phases I found most dangerous (WND was party-wide speed debuffs and Paralysis, which is HORRIFYING to my setup, and NTR had The Word For World Is Forest, which is the attack I found the single most deadly for him to use)