Hiruko converts the chakra absorbed from the Dark Release: Inhaling Maw technique into light blue flames, turning it back on his enemies with amplified strength to blow them away. The flames are expelled through the lower square of the mark in Hiruko's left hand.
The light blue flames seen in this technique are likely a reference to the "Will-o-Wisp," as the "Dark" (冥, kurai) in "Dark Release" (冥遁, Meiton) means 'gloomy; ghostly; night; underworld'.