One thing I feel kinda sad about with Kosuzu's run is the missed potential for Kosuzu becoming a mafia princess in all but actual title.

Because I just have this endlessly wonderful image of Yuuma stumbling across Ran's kit and having to deal with the awkward adoption because that tube fox obviously isn't mother of the year, here...

I've posted in the Discord about my Mastermind, timeline, and suspects speculation before so I'll post it here. The way I see it there are more or less, 3-to-4 'triggers' as I've been calling them that are needed to make the incident happen.
>Mastermind gains motivation
>Discovery of the Black Flames (I was told to not call this the Despair Sickness by the OP)
>Production of Burnt Cherries (seemingly the main vector of infection)
>Discovery of the Hollow Psyche spell/Zanmu's textbook is published. Is needed for diminishing the spirits of surviving Gensokyo inhabitants.
I say 3-to-4 because Burnt Cherry production might be the same thing as the discovery of the Black Flames. Either way in the current year. (Reimu 12, Kosuzu 10) There have seemingly been no public distribution of Black Cherries and while Hollow Psyche's exist, Zanmu's textbook on the subject hasn't been published.
Given that the textbook is published 7 years into the future, when Reimu is 19, and the Reimu from the last timeline is ambiguous older than current 12 year old Reimu, I think it's safe to assume that the Mastermind started the incident in the last timeline as soon as they got their hands on the textbook as discovered the Hollow Psyche spell.
As Yumeimei and Chiyari didn't get involved in events due to Reimu, I think it's reasonable to assume that the textbook or the Burnt Cherry Suwako was given. The second was seemingly piggybacked in Chiyuri, while the first seems more or less reasonable to have been transported through with a similar method.
Of course in the third timeline we have the book show up when Kosuzu is 3 and Reimu is 5. Of course the incident doesn't start, either because the Mastermind doesn't have either Black Flames or the method to mass produce Burnt Cherries, or due to the method of Yumemei time travel.
Either way, something is stopping them from starting the incident right now, but given how strong the girls are getting so fast, I don't expect things to stay that way for so long.
So whatever the Mastermind needs to start the incident are probably lining up, and I'm inclined to assume that it's access to the Black Flames & Burnt Cherry production being synonyms.

There is one more thing I'm suspicious about is what I call the Zanmu hypothesis. I.E, since in her first appearance Zanmu uses her power to empty out fairies, that if the mastermind has something akin to the crude oil of the Blood of Hell Pools, left over resentment curses, some form of material despair...etc, the mastermind could have or be planning to use Zanmu's power to empty out a large amount of fairies and fill them with liquid sadness and setting them on fire with the Black Flames.

One thing against the Zanmu hypothesis is that on the Discord VC Gooboi said that it was likely Cirno never became a Pyre in the last two timeline, or at least that us seeing her as a Pyre was very unlikely due to her mindset being antithetical to becoming one.
In other words, Zanmu's power to empty out fairies may have not been used. Although this is a big may, Zanmu's power is theoretically only needed to start the chain reaction. So it can be true her power isn't used to empty out Cirno and that her power is used to empty out a large amount of fairies.

>>19487
I think Y/Y has more missed potential, while kind of cool, I don't think there was really a set up for mafia princess Kozuzu. Compared to Y/Y that has Jenny-say-kwa, but it ends up not resolving that and leading into the next arcs bunch since that voters(I'm told) were more interested in Koishi. And while I like Koishi having an arc in a vacuum, it also feels like nothing was really solved there despite Koishi getting a resolution. Mainly because the situation between the Underground and Gensokyo isn't really resolved either.
Also admittedly, while I like the idea of Koishi's arc in a vacuum, in a continuing story we kind of have a less interesting Koishi now. They can't really do anything in Marisa's arc and any plans they may come up with are entirely hypothetical and neither of them have any real sort of planning or special ability set up. Koishi, besides being physically stronger then her sister, has the same ability.
So while I like them both, they're kind of both just there. I'm sure she'll prove herself eventually and finish her character arc but I'm kind of non-plussed with where she ended Y/Y in.