That sounds pretty promising for Youmu, how much damage are you outputting with her exactly? It seems like it'd be easy to take advantage of for the later Infinite Corridor bosses, since they tend to have ridiculous damage output and would surely drop Youmu to 1 HP.
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Reporting on my current progress, I'm on Infinite Corridor 100f, trying to figure out how to withstand Serpent of Chaos' "Disintegrating Breath" without losing any characters (I also need to level grind a bit, Iku 515 presently, planning on Iku 540 for the proper fight). I decided to skip the really strong equipment like Regalia and Medicine of Life up until now (besides the guaranteed Scourge/Long Sword "Ringil" from the 30/60f bosses), but offensively speaking, the game feels somewhat broken when optimizing damage output. Case in point:
https://www.youtube.com/watch?v=gIF9O-8pdLo (skip to 1:28). Almost a one-shot on Abyss Kogasa (she has 29m HP), and that's with a setup for status immunity (with a full offensive setup Tenshi can easily one-shot Abyss Kogasa). That's the most extreme example, but the bosses have generally gone down fairly quickly, even the enhanced final boss.
I've been messing around a lot with Akyuu, she's probably one of my favorite characters post-Awakening. Her resurrection skill, combined with how frail Plus Disk bosses are, is reliable enough that going max SPD for level ups is pretty usable, and she can still usually withstand at least one attack with a bulky equipment setup. Her Awakening spell card has 6000 delay and not 4000 like the EN wiki says (it's also 10 MP and not 11 MP, that's pretty minor though) and is also apparently bugged to apply a 1-hit invincibility effect to the leftmost slot of the frontline. The 50% Boost is enormous, especially when using two attackers. She doesn't have much else useful to do besides switch when Murakumo's Blessing is in use by Iku or Tenshi, but when it's not, she has more than enough MP to spare to repeatedly use World Shaking Military Rule (with the MP drain skill and Phenomenal Force of Will, she restores 7 MP per turn, presently she has 86 MP at level 524 with max MP Orbs/Gems and MP Boost), so I have her alternate between her Awakening spell card and WSMR.
I've also confirmed that Akyuu and Satori stack with their weakness damage boosting skills. The requirement to qualify as a weakness is an affinity of 80 or lower (red numbers), so for any boss that has an affinity like that, Satori provides more of a damage boost than racial bonuses (24% vs 20%). So far, only Abyss Marisa doesn't have a weakness like that (though a few other bosses have no weaknesses at all). Satori has also demonstrated herself to be fairly tanky and can actually withstand Serpent of Chaos' Disintegrating Breath with a typical tank setup (max HP in levels, First Aid Kit, 3x Long Sword "Gurenjihime", level 480, 525 library level) and no defensive buffs on her or offensive debuffs on SoC (she has about 530K HP like this and took 500K damage).
Sanae's (and Reimu's by extension) Super Youkai Buster appears to be a 20% damage increase as far as I can tell. This makes for a 40% (or 44% if it's 1.2 * 1.2, I believe this is actually how it works) damage increase against Youkai. This plus Power of the Living God for 30% more SPI damage makes her pretty good for increasing damage. Stacking the two together is an 82-87% damage boost all by herself, with the ability to buff stats with Miracle Fruit. Her MP restoring skill is also really solid, been able to grind almost indefinitely without much thought about MP management once characters start getting down to about half MP.
Best as I can tell, Murakumo's Blessing's skill Three Swords of Divine Era, the one that drains the user's spell card costs from the whole frontline and boosts damage by 16% for each, works as a separate multiplier for each one and doesn't add them together (1.16 * 1.16 * 1.16, in other words), for a 56% damage increase. Damage variance wasn't adding up for 48% when I was testing it, I was getting higher numbers than should've been possible. This was using Start of Heavenly Demise though (Iku with a -50% MND target so MND was a non-factor), which doesn't have a 100% confirmed spell card formula, so that might be the source of the discrepancy. It's a pretty ridiculous subclass either way, the damage output is enormous, and Start of Heavenly Demise is one of the strongest SPI attacks in the game.
For Tenshi and Iku...Tenshi's Awakening hasn't been as strong as I thought it would be, as Courageous Sword isn't worth specifically buffing her DEF/MND and bosses go down too quickly for Keystones of Spirit to accumulate to high numbers (usually, anyway). The higher HP from Seven Celestial Peaches is appreciated though. The biggest advantage she has is the variety of subclass spells available that scale off of ATK. In particular, Explosive Flame Sword, Puncturing Thrust, and Assassination Sword are all very strong subclass spells (Puncturing Thrust moreso due to its low delay for its damage than big numbers per hit), though of course personal spell cards are way stronger. The basic attack backed by Warrior seems to be superior to Shield Bash in terms of damage output (accounting for delay), while Samidare Slash is...kinda mediocre for a dedicated CLD spell card (and is stuck with an ACC penalty to boot). I haven't been able to afford enough SP to spare for Magic Counter+ on Iku to really try it out, but the damage boost from Orb of the Five Clawed Dragon is rather good. Accounting for leveling rates, Iku has one of the best MAG stats in the game post-Awakening (pretty much everyone with a better MAG stat levels a lot slower than her). Start of Heavenly Demise is superior in terms of damage to Iku's personal spell cards and allows her to deal SPI damage that competes with Tenshi's. Iku's Sorcerer backed basic attack is also capable of dealing out a large amount of damage with minimal delay, and only applying 10% of the enemy's MND in the formula makes it very reliable. Unfortunately, her MAG subclass spell options are rather poor outside of Start of Heavenly Demise, as Iku's WND/MYS options are better than Sorcerer's spell cards, Archmage's Southern Cross and Execution are too weak for their MP costs, and the rest are utility spells that don't do very good damage. This leaves Tenshi as the only attacker between the two for an enemy not weak to WND/MYS/SPI, and CLD/PHY seem lacking. Gotta try them out, but I'm thinking I might use a different character for those elements (Sanae for CLD and Momiji for PHY maybe).
Think about's about everything to mention so far. Probably gonna stop after Serpent of Chaos and wait for the next update.
