The Night Guy is a forbidden taijutsu of the highest level and can only be performed after opening all Eight Gates.
When Guy initiates the technique by saying "amass" (積, seki), he emits an enormous amount of red steam, the so-called "Steam of Blood" (血の蒸気, Chi no Jōki), and his chakra manifests into a red burning dragon around his body. Shouting "flow" (流, ryū), he then dashes forward at such an extreme speed that the space within the immediate vicinity of the technique is distorted, making it impossible for the target to defend against it. 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. The damage itself was so great that even Madara Uchiha as the Ten-Tails' jinchūriki thought he was going to die.
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 Uzumaki's use of Yin–Yang Release to restore Guy, the taijutsu master remained permanently disabled, confined to a wheelchair for the rest of his life.
While the other Eight Gates techniques combine a time of the day with an animal, this technique's name swaps the animal's name with Guy's own name, indicating that Guy became the dragon himself.