HunterxHunter:Tobirama's Journey

Nen and AuraAura Nodes and Awakening

Aura is the life energy produced by all living bodies, it is vital for survival and directly linked to one's stamina. The points on the body from which aura flows out are called "aura nodes". Additionally, aura is invisible to non-Nen users, it can only be seen after the aura nodes in the eyes are opened. Nonetheless, sensitive individuals can feel its presence without being aware of its existence.

In normal conditions, the aura from all parts of the body tends to flow together, producing one mass of energy. This happens without the individual's awareness, typically resulting in aura slowly leaking away from the body constantly without exceedingly harmful consequences and stemming up and off the top of the head. On the other hand, if someone whose aura nodes are fully open doesn't attempt to close them or control the flow of their aura, they'll soon grow so exhausted that they'll be unable to stand[8] or even lose consciousness. Learning to control one's aura nodes is the first step to becoming a Nen user.

People who have not trained in Ten will leak aura similar to water vapor boiling out from a kettle. It has been described as feeling like a warm, viscous fluid at rest, whereas powerful, refined auras produce a sensation that feels akin to needles pricking into the skin. Hostile aura generates extremely unpleasant sensations, which can cause a non-user to halt in their tracks and be unable to walk towards the source as if a wall had been erected in front of them.

Since every living being emits aura subconsciously, learning to sense aura is a useful skill for those who are trying to track down living things or searching for non-living things that have been infused with aura. An experienced user of Nen can judge the location and relative strength of their opponents by reading the output of their aura. On the other hand, skilled Nen users can also regulate the flow of their aura, so they appear to be beginners or regular individuals.

Grave wounds such as mutilations can disrupt the flow of aura in the affected body part and even stop it altogether.

Four Major Principles

In order to fully understand 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, and Hatsu.

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 while they are asleep.

Ten

Once a person has opened their aura nodes, they must learn to keep their aura from leaking away from their body. Ten 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 thin shroud around the user that feels similar to standing in a lukewarm, viscous fluid. Once it has been learned, it will never be forgotten, much like swimming or riding a bike. Despite being the most elementary technique of all, Ten is also one of the most important, since, together with Ren, it plays an instrumental role in determining the strength and smoothness of a Nen user's aura flow.

Ten maintains youthful vigor and reduces one's aging, since the energy powering the body no longer leaks away; one can then keep the body from breaking down and deter the aging process. Ten]is also the most basic defense against emotional Nen attacks, and it also offers limited protection against physical attacks, but hardly any when said attacks are enhanced with aura. Through frequent meditation and practice, one can improve the quality of their Ten and eventually even maintain it in their sleep.

Newborns with Nen instinctively learn Ten and Zetsu quickly to prevent fatigue.

Zetsu

While Ten allows a user to keep aura from leaking away from their body, Zetsu stops the flow of aura from their body altogether. By closing all of their aura nodes, the user is able to halt all outflow of their aura like water from a valve, making their presence much harder or even impossible to sense.

Shutting off the nodes in their eyes prevents the user from being able to see aura, but, since they are no longer surrounded by their own aura, they become more sensitive to the aura of others. The enhancement in perception is such that Zetsu can counter In, although it is not advised to employ it in this way. This technique is thus doubly useful when tracking another person, as it will make it easier to follow them and prevent other Nen users from noticing their pursuer. However, there are other ways to perceive a person hiding with Zetsu: aside from the effectiveness of the five senses, particularly perceptive individuals are capable of detecting the gaze of another person, although they might not manage to discern the position and number of onlookers. Furthermore, if Zetsu is activated within a certain range from a Nen user, that Nen user might notice their presence disappearing, especially if the Zetsu user's aura is powerful. Despite the technique not affecting vision directly, activating Zetsu in front of someone else will give them the impression that the user has turned transparent.

Zetsu can also be used to relieve fatigue, since it forces the body's external layer of aura to be fully contained within. For the same reason, it can be dangerous due to it leaving the body defenseless against any aura attack. Even a weak attack enhanced with Nen can do massive damage. Since even the thin protection offered by Ten is gone, a Zetsu user is also particularly susceptible to hostile emotional attacks, resulting in their mind becoming as vulnerable as their body.

Newborns with Nen instinctively learn Ten and Zetsu quickly to prevent fatigue.

Ren

Zushi using Ren

Ren focuses on outputting a larger amount of aura than Ten, projecting it outwards explosively.[3] This amplifies 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, albeit at the cost of expending said aura. If Ten is considered purely defensive, Ren can be regarded as its offensive counterpart, although it also grants the user vastly enhanced defensive abilities.

By tinging one's Ren with hostility, a Nen user can exert what is colloquially referred to as "bloodlust". Prolonged exposure to malicious Ren can induce uncontrollable dread, paralysis, and if experienced without the protection of Ten, even death. On the other hand, a neutral Ren can rarely be felt by non-users.[3] Since Ren is a show of power, it can also intimidate other Nen users, as it offers an approximate measure of the user's raw strength;[83] in fact, when someone asks "show me your Ren", they generally mean that they want to see the fruits of one's training, such as a Nen ability, rather than their Ren itself.[84] In most cases, Ren reflects the user's hostility without their control, and it can even leave faint traces in the environment after the Nen user has left the scene.

One can train their Ren to extend its duration and increase the amount of aura at their disposal. It is said to take one month to prolong one's Ren outside of combat by 10 minutes. With the right timing, Ten can be used to contain the aura produced by Ren.

Hatsu

Hatsu is one's personal expression of Nen. Its qualities are influenced by, but not restricted to, the Nen user's natural Nen category, one of the six available. Hatsu is used to project one's aura to carry out a certain function, creating a special and unique paranormal ability that is colloquially referred to as a "Nen Ability".

At first, Hatsu appears simply as a consequence of using Ren during Water Divination; however, it is more than a mere property of the latter, and it can be trained individually either through Water Divination itself, which seems to only affect the user's natural category, or by honing one's skills in a Nen category via specific exercises. Once a certain level of skill has been attained, the student can attempt to create their personal Nen ability.