The Night Guy is a forbidden taijutsu of the highest level, that takes the shape of a dragon, and can only be performed by opening all Eight Gates.
When Guy initiates the technique, he emits a huge amount of chakra. After gathering all of this chakra around his body — forming a red, flickering dragon-like aura — he dashes forward at such an extreme speed that the space (空間, kūkan) within the immediate vicinity of the technique is distorted, allowing him to bypass his target's defences. Guy then deals an immensely powerful kick which carries such force that it is capable of obliterating the target's body, as well as creating a devastating shock wave linear to the kick, capable of causing damage from afar.
The recoil was such that it completely shattered the bones in Guy's own leg. As a result of being Guy's strongest manoeuvre, following the attack are fatal repercussions as it left Guy on the brink of death; slowly turning into ash, crumbling from the immense discharge of his chakra. Because of Night Guy's effects, even after Naruto's use of Yang Release to restore Might Guy, the taijutsu master remained permanently disabled, being confined in a wheelchair for the rest of his life.