I believe the last part of the anime troubled a lot of people: What exactly happened? Why is it happening? etc.
The long blue haired lady is most likely Rika… or is it really her?
Considering her speech and stance, it isn’t Rika because she doesn’t have such powers, even if we are going far fetching that reaching adult age would “mature” her powers.
Remember what I said about Frederica Bernkastel? It is most likely her.
“Wait wait… I thought Frederica is the same!?” Wrong. As I already mentioned , Frederica is a complete different entity.
Frederica Bernkastel is an entity born from Rika’s “resurrection”: once “a” Rika dies, her consciousness is back in the Kakera world. From here, it is send back in another world to “fuse” with the destination Rika, overwritting her, and relaying the will and memories.
As you already know, “Rika” lived more than enough because of this phenomenon, and therefore, this consciousness or “collective consciousness” reached a state which it cannot be considered as normal. In the start of the Prologue of Minagoroshi, Frederica is hinting clearly that the “readers” are actually an emerging consciousness from the Kakera world, which she considers as “a brother or sister”. That alone proves that Frederica is “something” which transcanded mere memories and could have a singular consciousness aside of Rika’s.
In such case, what is her role here? Basically, Frederica was “another” witness of Rika’s struggle, though she was most likely much more close to the person named “Furude Rika” than Hanyuu. But unlike “Rika”, Frederica is wandering in the worlds here and there… on a whim, observing out of boredom. That doesn’t mean she didn’t care of all things that happened, but this is basically what “Rika” was: Furude Rika who “merged” with Frederica.
How this matter relate to her little trip with Miyoko? Frederica is the kind of entity who is having fun with all the possibilities and stories alike. As the game suggests, she got quite annoyed and bored by things repeating themselves (which is quite logical). Since Rika’s wish has been granted… “what if” the other side got hers as well…?
As shown in the end of the episode, Frederica wasn’t glad or so, but rather amused how fate changed.
What happened? Basically, Miyoko never knew her parents would go in the district to get her a flag, this is the very reason why she was alive until now. However, Frederica “intervened” but still warned what might happen if she recklessly accompanies them. This change merged with Miyoko’s wish and strong will to be always with her parents… that could mean she could have died in the accident. Instead, fate changed and it lead to the other probability: life for the Tanashi family. Come to the think of it, despite how the accident looked big, there isn’t any guarrantee that everyone died and so, especially we could see some “lightly” injured people.
How Miyoko’s actions could change this…? A simple change of seat, etc. Any action will have a cause and an effect, and both points were determined: Frederica’s riddle and Miyoko’s presence. The “certain” tragedy was undone just like this.
That said, is it really what happened? Isn’t it a time paradox? Ironically, no. As you must realize, the higurashi worlds are not on the same timeline. To be short, they are all parallel universe: despite we landed on the “happy end” in Matsuribayashi-hen, the worlds of Himatsubushi-hen, Onikakushi-hen, Tsumihoroboshi-hen, Watanagashi-hen, Meakashi-hen, Tatarigoroshi-hen, Yakusamashi-hen, Minagoroshi-hen, and the infinitisimal worlds are still existing on their own, dirfting with the tragedies. They are solid facts and realities, but they are not what Rika wishes for, and therefore, they are discarded.
As you might expect, in these worlds, aside of Watanagashi-hen and Meakashi-hen, the disaster happened. Therefore, usual things would happen, such like Ooishi and Akasaka investigating several years later (if Ooishi is alive of course, which isn’t the case in Tatarigoroshi-hen), Natsumi and her family who witness the outcome and the outbreak of the disaster in Onisarashi-hen etc.
Therefore, the world where Frederica is acting will not have any effect on “Rika” who finally reached her happiness after all these efforts. However… we don’t know if this “new world” without the tragedy for Miyoko will goes on in this way…
Do you want to know…? Well it might be interesting to see how a “perfect world” would go… the “WHAT IF” situation which is exactly what Frederica would be amused to observe, considering “Rika” finally got her wish granted.
How such perfect world would go on…? Well, that’s another story…