Hiiii! I finished Himatsubushi! So I finished the Question Arcs!!! It was a long road...
I'm happy nothing felt as scary as Onikakushi. Though... Tatarigoroshi was very triggering...
Himatsubushi probably didn't feel as mysterious for me because of Umineko
Since I knew from what Lambda said in EP6 that Bern was originally a piece in a gameboard made by Featherine, and that she committed a logic error and left Bern alone to solve it. Rika definitely behaved very close to Bern when she "changed"! I think that the explanation for she knowing everything is that her meta self has gone through uncountable games by now, trying to solve the logic error... though I wonder what's exactly the logic error in Higurashi. (Does this mean I can't solve it?)
As for the mystery, I think I have a human explanation for mostly everything! And I think the Final Mystery, the Big Culprit who kills Rika although she shouldn't die (though idk if she died in EP1) and that could be responsible of the Great Hinamizawa Disaster as well (does it happen as well in EP1 and 2?)... I think I know the whodunnit! But i really don't know what could be the Whydunnit...