Unnatural Mental Influence. it's an Exalted thing. TLDR version, something is messing with your head on purpose beyond just having really high Charisma scores.
edit: ninja'd.
It's not a thing. If it was a thing, this wouldn't even be a quest. It'd be a story where you get to see Sayaka's efforts all amount to absolutely nothing. It wouldn't be fun or interesting and would make for a terrible quest.
Maybe not a terrible story, but a terrible quest.
You don't need to worry about that.
it's less of a "I USE THE MIND CONTROL" (though that is also UMI, a very blatent example,) thing and more 'roll willpower to avoid the depression-aura the larval Witch in your Soul Gem is chenneling directly into your brainy-meats'- or someone using the magics to be more convincing, or whatever. in general, UMI is using some sort of Supernatural Bullshit™ to influence how you think or feel, beyond being just that good.
like, if someone has fucktons of CHA and speachifies 90% of a group into being his/her minions, you might then use a UMI spell to sway another 5-6% over to your way of thinking.
or the general Witchy Depression Aura, which is most definitely UMI. generally though, the hallmark of UMI is that it's subtle because any fool can throw it off if they notice and aren't completely out of willpower.
so yeah, I could totally see the Marshmallow using sneaky-subtle UMI to set off witchification-spirals, since Puellas aren't exactly bastions of willpower by design. Homu-chan's an outlier, because of the unique circumstances of her Time Bullshit letting her keep trying so she never really reaches the point where she witches out. this gives her the safety net she needed to get over her fragileness issues and become the adorkable obsessive Determinator we all know and love.
or what Greybitch was doing. see also: more than mind control, Glamor and Jedi Mind Trick for more examples.
Edit: for that matter, how you're described the effects of soul gem corruption thus far positively reeks of UMI. as it gets darker, it has a definite effect on their personalities and thought processes, which is pretty clearly a result of Magic Bullshit™ because said effect pretty much vanishes when they use Grief Seeds to hoover up the corruption.
It's not a thing. If it was a thing, this wouldn't even be a quest. It'd be a story where you get to see Sayaka's efforts all amount to absolutely nothing. It wouldn't be fun or interesting and would make for a terrible quest.
Maybe not a terrible story, but a terrible quest.
You don't need to worry about that.
[/grammar pedant]yes, sorry. my inner pedant had to clarify what I was talking about.
now, on to other, sillier things!
anyway, it's looking like we're going to have a freaking platoon of Puella come Walpurgisnacht, which is quite a bit more firepower than Homu-chan's ever had at her disposal. with that in mind, I predict that, much like the fight with Skadi, teamwork and numbers will succeed where random elements and a single manipulator have (repeatedly) failed. provided we can get organized and trained up sufficiently, Walpurgis should be less of an issue than Homura predicts.
that said, can we ask in advance if Homura's ever tried just nuking the fucking thing? we need to introduce her to the idea of getting bigger guns when the ones she has aren't shooty enough, and Walpurgisnacht definitely clears the godzilla threshold.
(...)
Did anyone noticed that the Bandwagon vote for "Go To Sleep" has [x[ Instead of [x]?