I'm quite sure I remembered fighting one of the 4 extra area boss that just instant death my Suika who had 100 death resist at least.
Considering that that was one of the extra bosses that did so, and I'm willing to believe that the extra boss's instant death attack is stronger at inflicting instant death than Komachi, who is an early game boss that is your first major exposure to said status ailment.
Also, a few things:
Wriggle: If I was to do anything about her, it would be giving her a skill that "adds poison to all attacks, if spell already inflicts poison, then it's effect is increased". I am aware that someone has a skill that does this already, but it's name makes it suitable only to Eirin(the current possessor of said skill "Pharmacist's Poison Mixing"), and not Wriggle. Perhaps a renaming of said skill would help in this regard? Also, I would replace Copious Vaccine(as her "Drug of Abuse" skill already reduces Poison damage towards allies) with Arm Twisting, as it would help her to inflict the Poison ailment more reliably(which is the whole point, really).
Kaguya: Firstly, why is "Robe of the Fire Rat" a skill? I mean, why would it be a bad thing to keep in spellcard form, like this...
Robe of the Fire Rat - Patient Mind
Fire Magic Attack spell
Targets all enemies
MP Cost: 6
Post Gauge use: 34%
Special Effect: Gives Kaguya a defensive version of the "Boost" status, thereby negating a portion of the next attack that would deal damage to her. This effect can be increased by leveling up the spell, making the spell into a sort of "instant shielding" against normally difficult to survive attacks, and while still dealing damage herself.
Additionally, since Kaguya has three spaces(Counting the removal of Robe of the Fire Rat from the skill section), I would add "Maintenance" and "Arm Twisting", at minimum. The former skill following the theme of "rare item collecter", as it will let her make the most of whatever she's equipped with(not to mention that she can a very slow leveling rate, so it's not as though it would break the game wide open if she had it), and the latter is for the fact that "Nation of the Noble Moon" does not cover elemental affinities. Of course, I could think of this skill instead of Arm Twisting...
Skill: Red Stone of Aja (yes, she actually does have a card based on this very stone)
Skill Point Cost: 5
Max Level: 2
As long as Kaguya is on the front line, all elemental damage dealt to enemies is increased somewhat.(Essentially the equal and opposite of Eiki's "Cleansed Crystal Mirror" skill)
Would that be better?
Mokou: I have said it once, and I will say it again. Give this girl "Arm Twisting", damn it! There are a lot of foes that resist Fire, and "Arm Twisting" is the one skill that would help in dealing with that problem.
Mystia: Seeing as one of her powers in canon is "control over winged birds and insects", I see no reason why Mystia shouldn't have a skill that lets her do more damage to Flying type enemies. Also, Beat Down sounds like a good thing to have.
...sorry for my rant, everyone. I just wanted to let all that out of my head. If it's too much, please tell me, and I'll stop.