One of the biggest mysteries in Umineko no Naku Koro ni: Who is the true culprit behind the mass murder incident on Rokkenjima?
The most popular theories amongst fans consider Ushiromiya Battler, the main protagonist himself, as the culprit. This is also subject of discussion in Umineko no Naku Koro ni Chiru, Episode 5 & 6.
Born out of these theories as a result is Dark Battler, who now officially appears in Ougon Musou Kyoku †Cross and the upcoming "Umineko no Naku Koro ni Hane"