A rare demon insect. After hatching, it is as thick as a chopstick. When captured and refined by a cultivator skilled in insect control, it gradually becomes finer until it is invisible to the naked eye, at which point it is considered fully refined. It is used to attack enemies, being colorless and formless, making it hard to defend against. Once it enters a host’s body, it will pierce the host’s heart at the Zi and Wu hours, causing instant death. It is difficult to determine the cause of death afterwards.