[Marion]

I personally like the idea that Bernkastel is the proven connection between Higurashi and Umineko. Reread her backstory, as told by Lambda, in EP 6 and it makes a whole lot of sense.

Spoiler for Higurashi Rei spoilers:

1) Bern was trapped in a situation that she couldn't find the answer to, but the logic error was clearly not her fault. In Higurashi the reason that the loops occur is because Hanyuu accidentally created one and couldn't figure out the answer. Rika was left to change fate on her own, while Hanyuu waited for a chance that never came.

2) Bern clearly hates her past and everything related to it, including Lambda and Featherine. Obvious enough why, but then there's the matter of why she isn't satisfied and seems more or less jaded.

3) The big part comes in with what happened after Bern escaped. If you relate to Higurashi think of it this way: Bernkastel and Furude Rika are two separate beings. They became separate officially at the end of Rei, when Rika decided to cut herself off from the rebirth cycle. We know what happened to Rika, but Bernkastel was the end result of the "other Rika", who was abandoned at the end of Rei.

Bernkastel won and escaped, but didn't get anything in return. She didn't get the happy ending she wanted and it was given to Furude Rika instead, with her being cut out of the picture entirely.

As a side note I find Bernkastel's past and possible motivations for why she goes out of her way to be incredibly cruel to be far more interesting than Yasu and her "lets blow up an island with 900 tons of dynamite because some boy forgot a promise about a pony".