Principles and Practice

in order to fully grasp Nen, one must first learn the Four Major Principles of the Shingen-Ryu school of Kung-fu. Everything else, including a practitioner of Nen's individual skills, is based on the basic manipulations of one's aura flow. The Four Major Principles, in order of study, are: Ten, Zetsu, Ren, andHatsu.
These basic techniques become second-nature to those experienced in Nen. For example, a beginner must learn to use Ten and concentrate to maintain it; whereas someone with experience will practically always be in a state of Ten, even during sleep.

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Ten

Once a person has had their aura nodes opened, they must learn to keep their aura from leaking away from their body. Ten (纏, Envelop; Shroud) is the process of keeping the nodes open, but also having aura flow through and around the body rather than away from it. Once maintained, it creates a shroud around the user that feels similar to standing in lukewarm, viscous fluid. Having a shroud of aura surround the body is the most basic defense against the emotional attacks from other users of Nen, however, it can't defend against Nen physical attacks. Ten maintains youthful vigor and reduces one's aging; since the energy powering the body no longer leaks away, one can keep the body from breaking down and deter the aging process. Through frequent meditation, one can improve the quality of their Ten.

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Zetsu

While Ten allows a user to keep aura from leaking away from their body,Zetsu (絕, Suppress; Null) stops the flow of aura from their body altogether. By closing all of their aura nodes, the user is able to stop almost all outflow of their aura like water from a valve. Since the user is no longer surrounded by their own aura, they are more sensitive to the aura of others. This can be useful when tracking another person and it will also prevent other users of Nen from noticing them. Zetsu can also be used to relieve fatigue, since it forces the body's external layer of aura to be fully contained within. However, since Zetsu involves shutting off one's aura, it can be dangerous due to it leaving the body defenseless against any aura attack. Even a weak attack enhanced with Nen could do massive damage.

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Ren

Ren (練, Refine; Enhance) is a direct application of Ten. Since a user is capable of keeping aura from leaking away from the body, it's also possible for them to produce more aura around themselves without having to worry about losing it. Ren focuses on outputting a high amount of aura and keeping it on the body, expanding the size and intensity of it. If Ten is considered to be purely defensive, then Ren typically what is used for offense. This increases the user's physical strength and durability and provides a large pool of aura for any advanced techniques or individual skills they decide to use.

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Hatsu

Hatsu (發, Release; Act) is the release or transmission of one's aura so it can be projected to carry out a certain function. In essence, Hatsu is one's personal expression of Nen that creates a special and unique paranormal ability (colloquially called a Nen Ability). A good Hatsu should reflect a person's own character; one can never truly master Nen if they only copy other people's abilities.