This pretty much just happen on the top of my head after I read Reisen's ending.
So after Reisen's ending, there's this particular line that got me thinking:
"Events similar to Reimu and Mokou's experience started happening one after another.
Humans would suddenly appear, seeming to have teleported. And other humans would disappear at the same time.
According to the humans who experienced it, it seemed as if someone had taken over control of their body.
But to outside observers it looked less like mind control, and more like people were switching places, body and all.
In a rather troublesome turn of events, everyone began to get used to this abnormal situation.
Some people even took advantage of it, saying that they could use the phenomenon to visit their favorite places whenever they wanted. This was one of Gensokyo's bad habits."
...Okay, this particular
paragraph. The line that said despite someone's using their own body to do thing, everybody seem to get used of it, and even used it to teleport to somewhere else they want. Make me think that the next game's theme is going to be the problem of agency vs convienience, unlike other game where the theme seem to be vague, and no more than "somebody's making an incident, let kick their shit". Such a clear different between game, more over on a spin-off, make me think that, aside from ZUN's kickin up his gear, this next incident is planned. Not just any kind of plan, a plan
to teach every single resident of Gensokyo a lesson. And who else could do that other than Yukari, the overlord mastermind herself.
At first I didn't even think of that though. I was thinking about the new boss and what would she be like, from her supposed ability to her goal. So far I seem to figured it out that the new boss's goal seem to be to revive herself, to make herself known, and to control every single person in the entire Gensokyo (what with the possesing theme and stuff). That would mess up the current rule of Gensokyo instigate and belong to Yukari, so I initially thought that Yukari would finally be in the next game to stop this. But then ZUN said:
"So tell me just this, is the new character one that has never been made it to the fighting games?"
"that's right"
That would mean that Yukari herself isn't going to join this,
despite this would shake up the very foundation of Gensokyo itself. So... what give? Then I remember that no, Yukari would want to shake up the foundation of Gensokyo, she even said it herself in Marisa ending. So if she want to, but didn't join the game, what would she do with the upcoming incident that would become an "absolutely horrible conflict"?
I then look at the new game again, see if I can find anything. I then remember, "Wait, in the title screen, isn't the color of the flower
purple? From my current clue and the fact that Yukari build her entire image on the colour purple, it would be obvious that not only Yukari would definitively have something to do in the next game, she and the new boss have something to do with each other. But to judge that Yukari have something just by the color of the flower would be a bit farfetch, so i tried to dig for more. Then I remember this:
"
http://www.mangahere.co/manga/touhou_ibarakasen_wild_and_horned_hermit/c035/18.html"
For those not interest in reading this, it's about Yukari's explanation of Humaned Away. Personally, I found the line of reasoning that the exchange would come from small to big is a bit of bullshit: If this is equivalent exchange, then what about all of the human she carried over, or just forgotten? Also why it doesn't become equivalent exchange right away, but go in increment? Also if only her dream come into here, then why it's going up ? There're some hole in this, but that's not importance. What I found interesting is this:
"What I do think is that someone is guiding her. I mean, being able to come here only in her dreams sound too good to be true, don't you think?"
At first, we think that line mean that Yukari known it was Kasen that's the cause of this. That now's still true, in the sense that she know "someone is guiding her", but she never specifically said it was Kasen that do it, only that her action right now is in line with what she want to do (which, if you remember, is shaking up the current status quo). That mean she's hiding that someone that actually done the Humaned Away, someone who have a relationship with Yukari, by blaming
Kasen for that. This still could be anyone, mind you, but...:
"
http://www.mangahere.co/manga/touhou_ibarakasen_wild_and_horned_hermit/c035/23.html"
Yukari then said to replace her with "dummy" of the similar dream state, kinda like how people have been replaced with "similar strange state" all over the place isn't it? I don't know about you, but I think it's obvious who exactly did she hide from all of this. (It's also a bit of an interesting comment by Yukari, saying that the people right now is only a "dummy" being manipulate by the status quo)
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TL;DR: Yukari is messing around again, this time she's involved with the new boss (either as accomplice, or they both used each other (except Yukari win the end game)), and this have been hinted all over the place.
I know this theory's a bit unbelievable, and the next incident is definitively going to be different from what I theorize. But looking at the clue I give to you, wouldn't this be stranger if Yukari didn't involve one bit in this entire incident? Especially if it's to teach everyone the lesson about Agency vs convenience, the problem that have secrectly plague Gensokyo, and Touhou in general?