This is a partial transcript of an interview between Ryukishi07 and Keiya, author of several Umineko guidebooks. Original English translation sourced from here, and Chinese translation sourced from here.
This article or section contains untagged major spoilers for all of the original Higurashi no Naku Koro ni, possibly including the console-exclusive arcs. Readers who have not completed the main story are advised not to proceed further.
K = Keiya, the author of Umineko speculative guidebooks 「うみねこ」真相解明読本.
R = Ryukishi07
R: ... To examine [Beatrice's] thought process and motive is an interesting direction in terms of finding out the fate of the world of Umineko. When thinking in that direction, several of the unsolvable elements in the story might actually be solved. Perhaps this is what Lambdadelta meant by "weakness"; Lambdadelta is very angry about this.
K: The appearance of Bernkastel and Lambdadelta serves as a fanservice, but also seems to have other meanings. It looks like they are somewhat connected to the core of Umineko.
R: Which portion is fanservice and which portion is proof of the distortion created from human objectivity is hard to say. I admit there's a character named Bernkastel in Higurashi, but I don't remember there being a character named Lambdadelta. Why does anyone think [Lambda] has appeared in Higurashi? When human beings encounter an unknown thing, they would automatically regard it as something that exists in their memory. Those who've played Higurashi might have directly fallen into a trap. Those who haven't played it would think [Bern and Lambda] are two ordinary witches. Bernkastel and Furude Rika look similar, so people would think they are the same character. But Lambdadelta and Takano Miyo look nothing alike; they only have similar bangs and eye colour.
K: When those two appeared, they've mentioned the "previous game", but they didn't specifically say it's Higurashi.
R: Yes, you've noticed even that...
K: In Higurashi's Matsuribayashi-hen, Hanyuu told Takano the method to become god. "Sacrifice one's life with heated iron (translator's note: as in a gun, I think), and one would ascend to godhood." There's a line like that, I think. Then with that we can kind of understand the relation between Lambdadelta and Takano Miyo. Even though they aren't the same character, this association is interesting enough.
R: I think you can think about in what position do these two witches enter this game. Only one point is certain: they are not the players. The players are Beato and Battler. [Bern and Lambda] are merely observers. Observers are like soccer fans: they only support the team they like. Which means, Bern might be Battler's ally, but it's better to be wary of her. Even though many people completely trust Bern, in ordinary cases, when this kind of dodgy character offers to help for free, it definitely looks suspicious. In EP3 Hidden Tea Party, I only saw her urging Ange to jump off the building; I haven't seen her acting nice at all (smile).
K: You have to look at things in all perspectives.
R: Exactly. Lambdadelta isn't completely an enemy either.
K: Let's not talk about the connection with Higurashi for now. The concept behind "the Witch of Certainty vs. the Witch of Miracles" is interesting. In a previous interview (translator's note: from one of the Umineko guidebooks), you've said that human beings call the behaviour of automatically converting an event with 99.99% certainty into 100% as "certainty", and call the behaviour of not denying the remaining 0.01% possibility as "miracles". It looks like this statement is closely related to the present design.
R: Yes. If you think of it that way, it is worth paying attention to which part of the chessboard is 99.99% and why not 100%. Digressing from the topic a little, in essence, why is there a need for an advance notice to the murders? If the goal is simply to kill people, then there's no need to write an advance notice; it's good enough to just quietly kill people off [...] Why following the epitaph and committing all those flashy murders? After a mass murder has been committed on the first night, everyone would obviously gather together and confine themselves. It gives me a headache trying to figure out a plot to separate the characters (smile).
R: Ordinarily, when coming up with the plot, you would want to make it so that "everyone is killed at once" [...] if the body was discovered then it would only attract more enemies. But to deliberately committing such attention-grabbing murders, this in itself must have a reason. The author keeps stating the murder methods in the EP3 TIPS for those victims whose death is unclear. That author must've been thinking about this: why is it necessary to commit murder according to the epitaph? The witch's letter has also said that as long as the epitaph is solved, then the killing would stop. It's supposed to be killing for the sake of killing, then why is there a possibility for interrupting the killings? Perhaps the existence of a magic named "Beatrice" has a method of 100% killing off the people on the island, but it stops at the 99.99% stage. Now Eva has survived. Why does the culprit (or culprits) automatically stopped at the 99.99% stage for something that can be accomplished with 100% certainty? Kirie called that "pride". When you look at the three serial murders up to EP3, you can't even tell what the culprit is thinking. Perhaps it's like the Rule X, Y, Z in the Comiket booklet. Even Bernkastel doesn't understand the rules. Maybe the truth will be left in the dark. This is the time to turning the chessboard around. You might find something by thinking about "the reason behind the culprit's action"...
R: [Concerning locked rooms] The somewhat more interesting theory is this: "In the Eva/Hideyoshi locked room from EP1, the door chain is a bit long." There is no conflict with the description in the game, and it is a locked room. All [the culprit] have to do is reach between the door gap and take off the door chain (smile). Even though this is not the truth, it's an unique theory.
R: [Concerning the additional characters who appear on the island] Originally in a closed environment [as in Rokkenjima], the number of people should remain constant. This island should be closed, but the number of characters to appear are increasing. This contradictory situation is quite meaningful.
K: Some readers believe that these are hints. "The number of characters in a closed environment should not increase, but it did. And that's because..."
R: You can think that people from the outside have come to visit, or maybe there are people hiding in the island. [...]