I've found it strange Rika didn't included Hanyuu when she said "thanks to the clubmembers she finally triumphed".
The other thing that started to bug me comes after when she wokes up in the next world. I may be totally off and laugh how far is my crazy theory when I watch next episode, but I actually think, that world is a continuation of the epilogue when Frederika/grown Rika (I'm still not sure which she was supposed to be) prevented Takano's real dad to get in the bus accident, so she didn't pursued old Dr. Takano's research, as she wasn't an orphan.
The proof that Dr. Takano was interested in the syndrom here on that world too, is how he founded/had some relation with the people who founded the clinic, as they/he named it after him. By that logic if the syndrom wouldn't exist in that world, he probably wouldn't have been that interested to scientifically research a completely normal small town.
Therefore the project to station a research team in Hinamizawa didn't happened, because nurse Takano (what was her name Miyano or something, I'm so forgetful with japanese names of the unsympathetic characters) didn't even know the existence of him and he didn't had any capable successor. As the Tokyo group was not established here, they didn't kidnapped the minister's son, so eventually the Dam construction got approved (that's the theorys weakest part, gonna elaborate it at the end)
Because the opposition didn't went far (I assume the Tokyo group supported the whole opposition, more on that later), the Houjo family escaped their role as a scapegoat, that's why satoko didn't killed her parents because no one bullied them for supporting the dam. Of course because the Houjo parents are still alive, Satoshi-Satoko didn't moved in with their uncle (to Bel Air. And they didn't whistled for a cab. Haha I couldn't resist
), so Satoshi didn't went berserk here either.
Because Hinamizawa going to be a lake next year, K1's family probably moved to a different peaceful town, as it's unlikely they want to move here for such a short time only (I reckon the government wouldn't even allow it anyway).
Further proof that the syndrome exist is how the superstition was present that they shouldn't move anywhere fearing from Oyashiro's wrath. (The scene actually hints that Rika's parents are probably still alive. I honestly don't know why she couldn't be happy to see them again even if for a short time only. Especially considering when could have been the last time she seen them...)
If I assume everything so far, what I don't understand is the following:
Where is Hanyuu here? She isn't related in any way to nurse takano's early days.
If we assume the hinamizawa syndrome exist (it is heavily implied) the demons which inhabitated Hinamizawa centuries ago (I assume they are Hanyuu's race hence the horns) should have existed here too. I've found it actually strange that Rika was rather looking for K1 before trying to find her long time companion Hanyuu. Probably we gonna find out next episode though, hauhau nano desu~.
What I mentioned before and I still don't understand fully, is 5 years ago when the residents was opposing the Dam construction -even if it was weak-. (mind you I may be remembering that wrong, I watched it quite some time ago) The very first killing aka the Dismemberment of the Dam supervisor was not the action of the Tokyo group (they wouldn't have kidnapped the minister son than).
As far as I remember it happened because the workers went nuts, supposedly because of all the hate and resentment from the opposing residents caused the syndrome to escalate. But they opposed here too! So why didn't the first murder happened here? I assume (assumed before) that nurse Takano's group were supporting the opposition against the Dam construction and probably stirring up trouble to both parties in order to gain time and they could kidnap the minister's son. What I don't like in that part of the theory, is how we didn't seen any firm proof wether the Tokyo group where supporting the opposition in any way or not.
Uh such a long unrefined post, sorry about it, my mind is still a bit fuzzy.