Umineko no Naku Koro ni EpisodeX Rokkenjima of Higurashi crying (うみねこのなく頃に EpisodeX ROKKENJIMA of Higurashi crying) is a manga-exclusive series written by Ryukishi07 and Koshiko Miyagi, and drawn by Yuki Hiiro. Essentially a cross-over between Umineko When They Cry and Higurashi When They Cry, it features characters from both series.
The series was serialized in Dengeki G's Festival! magazine by ASCII Media Works, a brand company of Kadokawa, between January 26, 2009 (shortly after the release of Alliance of the Golden Witch, notably) and February 23, 2011. Two volumes of EpisodeX were released: the first on February 26, 2010 and the second on April 27, 2011 under ASCII Media Works' Dengeki Comics imprint.