I think I just figured out the backstory of Bernkastel and Lambdadelta from Umineko When They Cry.
We have all assumed Red Eyes Satoko was Lambdadelta yet what if that is not the case just as the Writer hinted?
What do we know of Red Eyes Satoko? She claims to be the Real Satoko nothing more.
What do we know of Lambdadelta? Eua blatantly assumes Satoko is her and that she lost her Memory? What if she was fooled?
Rika has a Red Eyes mode she didn’t have in the Main Timeline which is suspicious. What if that mode is Lambdadelta?
Why would Lambdadelta possess Rika? Because she is Vier Dreissig and to inhabit the Body of a Tomboy Slacker would be a nightmare for a Genius like her.
Of course that means that Fragment Rika/Bernkastel’s confrontation with Lambdadelta doesn’t happen in Gou/Sotsu but after that when they get caught in a Logic Error without Rika’s Game Master Eua to help her.
Fragment Rika eventually figures out that Lambdadelta is not her and kicks her out of her Body forcing her into Fragment Satoko’s Body and gets promoted to the position of Witch of Miracles.
This leads into Umineko when Fragment Rika/Bernkastel and Real Rika/Featherine gets in contact with Ange upon winding up in detention with her for bad grades(thanks to Lambdadelta’s absence depriving both of them of genius) and gets her in contact with Fragment Satoko who discovers the Rokkenjima Massacre.
Lambdadelta promptly turns Fragment Satoko into Beatrice the Endless Witch and starts Umineko while Bernkastel makes attempts to defeat Beatrice while giving the Rokkenjima Games an unhappy ending.
Irony how Fragment Satoko gets abused and mistreated by both Real Satoko and Lambdadelta/Vier Dreissig.
Now we come to Hanyuu’s role in Gou/Sotsu: In the Main Timeline it is made clear that Hanyuu has nothing to do with the Hinamizawa Syndrome while the Outbreak Timeline and Gou/Sotsu Timeline outright states that Hanyuu is responsible. Furthermore the Sea of Fragments has said Fragments originally be called Memory Fragments.
Real Satoko, Eua/Featherine/Real Rika and Hanyuu are delving into the world of Memories and both Rika & Satoko are messing things up for one reason or another.
Hanyuu’s role is to replicate the events of Higurashi then leave while Vier gets Rika & Satoko(whom she is supposed to possess) the answers to Saint Lucia’s Schoolwork.
Everything goes wrong when Vier goes for Fragment Rika going Off the Rails leaving the Real Rika with no means of getting answers for Satoko and getting bored thus making her willing to turn the Hinamizawa Memory Fragments from a simulation into an outright boardgame to watch due to thinking Vier is Fragment Satoko and had lost her memories rather than realizing that she is possessing Fragment Rika.
And we still don’t figure out Vier’s role in Ciconia aside from her attempts to figure out the nature of the Une Virus(which judging from the traits it give Memory Fragments when giving them a Dark Awakening is the Hinamizawa Syndrome).
Considering Vier is a Time Traveler(and seen by Ange as on a level higher than Bernkastel) it is easy to assume she created the Sea of Fragments in present day to deal with Une/The Hinamizawa Syndrome using Simulations while Rika, Satoko, Hanyuu, Battler and Ange used it for themselves for selfish reasons which in Rika, Satoko and Hanyuu’s case is due to the Hinamizawa Syndrome(we never see proof that Hanyuu was ever cured despite the damage to her horn removing obvious symptoms).
The problem is that Vier herself is infected with Hinamizawa Syndrome making her one of Une’s pieces just like the real Takano(not to mention literally everyone using the service except Ange and Battler).
Speaking of Ange and Battler: after Battler’s original persona dives into the Sea of Fragments with the Beatrice illusion that Fragment Satoko set up the Illusion and all the pieces of the Rokkenjima Game Board are all contained within the Rokkenjima Cat Box while Rika in the form of Ikuko preps Battler for implanting into Ange’s head with the entire Rokkenjima Game Board and all of it’s pieces.
Beatrice in Ange’s Head is now using Ange as a base instead of Fragment Satoko. Real Satoko doesn’t get involved at all in the Umineko story letting Vier(who serves as the base of of Eva who might very well be the true identity of Vier herself considering her knowledge of EVA-Beatrice and concern for Ange), Bernkastel, Ange, Battler, Rika and Hanyuu(the base of Maria and Rosa to the point of providing the voice for Maria) move the pieces around.
Edit: You know putting Eva as Vier’s true identity might get us the real answer to the Rokkenjima Murders:
George and Hideyoshi’s deaths? Possible and understandable since she now has a different Husband and Child whom she loves more than those two. And that’s only assuming Ciconia is the actual future rather than a Memory Fragment where she tests a plan to get Ange/Meow(who is sharing a Body with Battler/Miyao after Umineko) possessed by George/MIYAO.
Shannon and Beatrice having Tattoos like Eva?: They are Eva after she became Vier Dreissig.
Battler seemingly confirming Beatrice’s demise? She can mess with memories easily with her technology and is now an immortal Superhuman thanks to self-experimentation.
Eva gets more terrifying because of this.