By utilizing the a Byakugan's ability to see chakra as well as the chakra pathway, Hei slashes at the different points that act as "limiters" to a person's body. By doing so, she unlocks the opponent(s) full power, and voluntarily gives them the ability to utilize the basic principles of the Eight Gates. However, by doing so, she speeds up the amount of time it would take the opponent's body to expire. In other words, while giving them a temporary boost in power, she actually spells the end of their life, by breaking down the very limits that allow the body to preserve itself for a longer period of time.