The Dark Release (冥遁, Meiton, Viz: Shade Style) is a combined nature transformationkekkei genkai that can be used to absorb, manipulate, and release chakra taken from an opponent. Hiruko used techniques of this nature through a mark on his left hand. This mark resembles two diamonds, one overlapping the other. Chakra is absorbed through the upper square, while it is released and manipulated through the lower. It is unknown what elements this nature entails.
The kanji used for "Dark" (冥, kurai) does not directly mean "darkness". It is more related to "gloomy; ghostly; night; underworld".
The mark on Hiruko's palm also appears on the back of Hiruko's Teamhisthreesubordinates, suggesting that it is rather related to the Chimera Technique.
It is possible that Hiruko sealed the kekkei genkai into the Chimera mark, which would explain the method through which it is used.