You really like the skill arm twisting hehehe.
In all honestly, Maintenance would probably make Kaguya OP. Considering Kaguya already has one of the high MAG and MND growths in the game, Maintenance (although renamed Rare Item Collector) would be... broken on her. You also have to consider that Kaguya has the best overall elemental resistances in the game (every element except physical is over 100) and giving her maintenance... oh my god. Nitori is already very good with maintenance, becoming a bulky speedy attacker nuke thingy, and putting maintenance on Kaguya would just... break her, I swear. With the right items she would have EVEN HIGHER elemental resistances, sky high Magic and Mind and MP, moderate speed, HP and Defense, and just so strong. Plus if you gave Robe of the Fire Rat and Stone of Aja along with "Rare Item Collector" and Arm Twisting, She would just be the best mage in the game hands down. Mystic, Spirit, Nature, Fire attacks, ignoring 90% of Mind, ignoring some elemental resistances, quick back seat recovery, and "rare item collector", that's just broken. Kaguya is honestly fine the way she is. She's already quite strong now. (Kaguya may be my fav Touhou, but I don't want her broken.)
Okay, let's start.
1. I wanted to replace Robe of the Fire as a skill with Red Stone of Aja, mainly so that she would give a minor boost to everyone while in battle(it's not supposed to be as strong a boost as what the mono-element boosting skills(Magic Training, Blazing, etc.) would offer).
And yes, I actually do like Arm Twisting, considering that it's one of the better skills in the game. If it's considered broken on Kaguya, then maybe...
Related question: Does Easygoing increase how much you heal while in reserve? Because I could see it fitting Kaguya somewhat, if only thematically...
Also, do you think that my "Robe of the Fire Rat" as a spell was OP? I would like to know your thoughts on that.
You want to add arm-twisting to Kaguya's existing ability to basically ignore defense? So, in other words, she'd have entirely nigh-irresistible attacks. That's just silly
Maintennance would also make her OP, yes. The characters with it have pretty meh stats and become amazing as it is, already.
2. I honestly wasn't aware of how Powerful said skill was, actually. I simply saw the skill as a sort of a "this skill fits Kaguya's theme of using rare items, so it's good" thing.
Basically what I'm getting at is, suggesting improvements that make characters much better, is out of place if the character is already good. The suggestions for Wriggle and Mystia are less out of place though, yeah. Arm-twisting doesn't sound very character fitting for Wriggle, but it'd make sense on Mokou... although Mokou already has a pretty amazing skillset and several things to help her damage, and she does possess a WND spell with cool offense debuffs (albiet it's probably not that good offensively on bosses; not that I've ever built her offensively because she's a godly tank)
Honestly, even with arm-twisting, if a boss resists fire it just wouldn't be worth using Mokou as a nuker in the first place, so it'd be a moot addition. On Marisa it matters more because A.She has no purpose but damage, and B.Master Spark is silly (and she doesn't even have a single other element in her arsenal, like Mokou's wind spell that can be used for randoms at the least in an offense build) and Kogasa's terror infliction is already pretty insignificant even -with- armtwisting, so it really needs it to not be totally pointless. Utsuho is pretty meh so arm-twisting helps her not be garbage in half the battles even for people who do attempt using her. Wriggle is mono-nature and relies on poison even still, so it'd be a good idea on her, but it doesn't make much sense in-character.
3. Serela, the sheer fact that fire element is resisted as often as it is is the reason for it, not to mention the fact that the side effect of her wind spell(ATK and MAG debuffs) would be easier to land with said skill, so it helps a bit as a skill that makes her able to try to deal damage while being the tank that she is.
4. Unrelated to my posts, but related to the "Patchouli is weak as crap" argument: did you guys test her spell when they were at maximum level, or just at starting levels? I know that it's a stupid question, but it would be nice to clear that up before continuing the debate, so that it's not a factor in all this.
5. Also, as for Wriggle, I honestly couldn't figure out anything that that would help her in inflicting poison, other than my suggestion of a skill that "would inflict Poison with all her attacks and increase the strength of the Poison for those attack that already do", so it was a matter of mechanics more than flavor.
6. I know that I think that I've said this before in some way, but has anyone tested the Sorcerer subclass on Sanae? Given it's perk of boosting row attacks, I could see it helping her actually do some form of damage with her CLD element spell, the spells in there give her access to WND and MYS as attack elements(which is strangely appropriate, given that this is Sanae that we're talking about), and the stat boosts that the subclass gives can only help her, regardless of her build(as if she has more than one).
Also, as a related comment on her, would giving Sanae the "Grand Incantation" skill make her OP? I know that it would fit her thematically, given that her power of miracles requires time and stuff like that for a stronger effect in canon, so this skill would kind of emulate that. The skill itself would make her attack spells viable for offensive purposes and give her healing spell a powerful boost(Although I still don't get why it can't cure Heavy. It should, in my opinion, since it isn't like it would make her OP or anything to be able to do so), so she can be seen for more than her "Miracle Fruit" spell. Just charge up and then cast. Not the same as the other healers, but good enough, yes?
That's all I got for now...