First of all, who is Frederica Bernkastel?
Frederica Bernkastel (Frederika Berunkasuteru) is a mysterious character, appearing only once in person in Higurashi no Naku Koro ni Kai, in the last episode of Matsuribayashi-hen. There she speaks to a young Takano Miyo, as she now enjoys travelling to different worlds and playing with the "pieces" in them. Frederica looks very similar to Furude Rika, and it has been suggested she and Rika are either the same person, or she is a compilation of all the past Rikas who died. This is implied in Matsuribayashi-hen that when talking about Rika she refers to Rika has "I" or "me".
There is also a theory that states that Frederica was born from Rika's despair, hopelessness, and loss of interest in breaking fate after Tsumihoroboroshi-hen, since in the sound novels, Frederica tells the reader, "Eventually, she started giving up, and lost interest in those worlds. That's how I was born...". If this is true, it also relates to Bernkastel of Umineko. This would directly explain Bernkastel's declaration of being a separate person from Rika, Bernkastel's empty eyes (a.k.a. loss of humanity, she has no glint or life in her eyes), and her (ironic) title as the "Witch of Miracles" (Bernkastel says that she is named the "Witch of Miracles" because she is the only one who truly knows that miracles cannot occur out of the blue by mere praying ((this concept is proven by Maebara Keiichi in Minagoroshi-hen)), while Rika used to immaturely keep praying for miracles to come her way without taking action). Either way, she and Rika have a close relationship.
There is a possibility that Frederica was involved in putting Rika through the terrible fate of a perfect world. When she appears for her first (and only) time in Kai and meets the younger version of Takano Miyo, she asks Takano whether she wants to "live or die"; Takano first tells Frederica that she wants to live, so Frederica told her, "You may go to your friend's house. However, she will not be there." Upon hearing this, Takano changes her mind and says she wants to die, so Frederica tells her to go follow her parents, so Takano can earn another flag from a mall restaurant to add to her collection. The "live or die" part may have meant if Takano wanted to "live" a new life as Miyo Takano, or let that identity "die" and stay as Tanashi Miyoko. Takano says she wants to "die", so she continues on to the mall with her parents. It is revealed in the last episode of Kai that Takano and her parents boarded a different bus than the one fated to crash. Thus, Takano and her parents are not led to their deaths, Takano does not change her name to "Takano" or ever meet Hifumi, which may have been a trigger to the perfect world where the Irie Clinic is never established, Tokyo never involves itself in Hinamizawa, and none of the characters suffer any tragedies. Saikoroshi-hen could possibly be that world where Frederica stepped into, and could also be interpreted as Bernkastel experimenting a fate where she got rid of Lambdadelta's major piece (Takano) beforehand as a pre-emptive move to create a desired heaven for Rika (of course, even so, things don't happen as nicely as expected for her).
In the Higurashi no Naku Koro ni Rei novel Saikoroshi-hen, Rika uses the name 'Frederika Bernkastel' for the first time, in order to distinguish herself from the 'Rika' of that world. However, at the end of the novel she undestands the meaning of Hanyuu's power, and gives up on it, choosing to go back to being just 'Furude Rika', a normal girl with no powers. She also said that the part of her who lived for 100 years and pulled the strings of fate—Frederika Bernkastel—will continue to exist in an higher world. In Higurashi, she writes poems that appear at the beginning of every arc, though they are absent in the anime and therefore many people have never heard of them. Her poems give the over-all theme for the upcoming story and document Rika's struggle through the different worlds. It is shown in the manga at the start of Minagoroshi-hen that Frederica meets Rika in the world of kakera, where they discuss the three rules that constantly appear throughout the universes:
- Rule X: A random person in Hinamizawa succumbs to Hinamizawa syndrome and is driven to acts of violence by extreme levels of paranoia. Keiichi, Rena and Shion are the most prominent victims of this rule, as at least one of them develops Hinamizawa syndrome in most scenarios. For example, in Onikakushi-hen, Keiichi becomes suspicious of his friends and comes to the conclusion that they are the perpetrators behind Oyashiro-sama's curse, causing him to beat Rena and Mion to death out of what he thought was self-defense. In Watanagashi-hen and Meakashi-hen, Shion becomes suspicious of the Sonozaki family's involvement in Oyashiro-sama's curse, and is convinced that they were responsible for the disappearance of Satoshi, causing her to kill Oryō , Mion, and anyone else who she considered to be responsible for amplifying Satoshi's pain(including Rika and Kimiyoshi, who she believed were also involved in Oyashiro-sama's curse, and Satoko, who was a burden on Satoshi). In Tsumihoroboshi-hen, Rena also becomes suspicious of the Sonozaki family's involvement in Oyashiro-sama's curse, causing her to take the school hostage. She then threatens to blow up the school in an attempt to force the police into negotiating with her.
- Rule Y: Jirou Tomitake and Miyo Takano are killed on the night of the Watanagashi festival without fail in every scenario. Frederica considers this rule to be more stable than rule X, as the method of killing is consistent in every universe, meaning that this rule is absolute, caused by a powerful and unwavering will. Although this rule is independent of rule X, the deaths of Tomitake and Takano usually act as a catalyst, which causes paranoia in Keiichi, Rena, or Shion, and triggers rule X. This occurs because they try to relate Tomitake and Takano's deaths to their own perception of the curse. For example, in Onikakushi-hen, Keiichi believes that Tomitake was killed by the villagers because he was an outsider, and that he will be next, because he just moved to Hinamizawa recently. In Watanagashi-hen, Meakashi-hen, and Tsumihoroboshi-hen, Shion and Rena believe that Takano was killed by the Sonozaki family for knowing too much, which fuels their suspicions. The person with the strong will that causes this rule is later revealed to be Takano, who kills Tomitake and fakes her own death in every scenario.
- Rule Z: Everybody in Hinamizawa believes that the Sonozaki family is responsible for the series of mysterious deaths. The Sonozaki family actually has no control over the deaths, but uses Oyashiro-sama's curse as a bluff to scare everyone. However, because of the assumption that they are controlling everything behind the scenes in Hinamizawa, everyone immediately comes to the conclusion that the seemingly coincidental deaths are all connected, and that Oyashiro-sama's curse is a system created by the Sonozaki family to eliminate the village's enemies. It is the very existence of the "curse" that causes mistrust amongst the villagers. The mistrust breeds suspicion and paranoia, which ultimately leads to the acts of violence caused by rule X. Though they may differ somewhat, Keiichi, Rena, and Shion's perceptions of the curse all have one thing in common; they all suspect the Sonozaki family(or in some cases the entire village). This rule is enforced by Oishi and Takano, who contribute to fueling paranoia in Keiichi, Rena and Shion by telling them about Oyashiro-sama's curse and the Sonozaki family's apparent involvement in it.
Well, that's it from me, after haven't posted anything at all this long...
See you another chance!!