These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Gensokyo 20 XX
Designated Villain: Played with to a degree. Seeing it from her perspective, Yukari was seen as this to a mild extent during the events of Mine because she refused to give back Reimu once her duties as wet-nurse were exhausted, which were to be expected as she took care of her since birth, thus she's grown to be attached, seeing herself as a mother figure to "her little human child". Reimu can never forgive her birth-mother for "demonizing" Yukari.Unlike most examples, she is seen in a more sympathetic light, especially if you take into account that she is unable to bear children of their own and hasn't caused anyone any harm to warrant anyone's hostility, aside from refusing to give Reimu back to her mother initially once her deeds were exhausted.
However, Amoridere swings between both Reimu's mother and Yukari as being designated villains, if either side is taken, as both are at fault, as she's stated in her own words.
Fridge Horror: Done In-Universe. Mokou did ask the question as to what would happen to Yukari once the warden gets tired of her and did say what would be likely.
What happened to Yume? We never do find out what happened to her but we do know she died. Actually, we're never going to find out as she was cremated soon after death.
Was Reimu brainwashed and what is the effect of said mental scars?
Genius Bonus: According to most Japanese folklore, a kerakera-onna is the ghost/youkai of an abused prostitute rhat only made it to middle age.
Moral Event Horizon: Everything the warden does is treated as this, especially when he has Ran scalded to the point of being scarred on top of separating her from her babies, all of which die, has a small child injected with needles every three hours for screaming and then presumably brainwashing her, and making Yukari his lover, something that has everlasting effects on her.
Seiji Kijin, aptly called Seija the Motherfucker when she attempts to brainwash Yukari into killing Reimu, Shimmy, Chen, and Ran's babies just because she sees them as a hindrance, nevermind the fact that she is the reason as to why resources are running scarce. According to Yuyuko in a few Noodle Incidents, Seija also seems to have a killing streak, seeing that she's caused more than a few deaths.
The Woobie: Everyone is this but the ones that really this are Reimu, Chen, Rumia, and Eirin
In Reimu's case, she's more like an Iron Woobie, as she is more than willing to put everything aside and endure hell, even going to hell and back, just to look forward even if she was facing the prospect of dying.
Then there is Ran, who is burned with scalding liquid to the part of scars, all for snooping, and had lost her whole litter of pups, three to miscarriage, and three after they were separated from her.
Then we get Yukari, who allows herself to be "abused" at the hands of the warden, in exchange for the other's safety and it is a fairly safe assumption that before they see her again, she would be broken and, to make it worse, she had gone insane before. To a Tear Jerker degree, Satori notes how they may not get "Yukari" back.
Recently, Eirin's woobiness is was taken Up to Eleven in Gensokyo 20XXIII and we found out her reasons for suicide and they are, to summarize, her life is hell.