Nen (念, Mind Force) is one of the defining features of the manga Hunter × Hunter by Yoshihiro Togashi. It is a technique that allows a living being to use and manipulate their own life energy (known as aura). The word "Nen" can also be used in conversation to refer to aura.
Properties of Nen
Creation and Use
Aura (オーラ) is the life energy produced by all living bodies vital for survival. Aura from all parts of the body has a tendency to flow together, producing one mass of energy. This happens without the individual's awareness, typically resulting in a slow leak of aura continually escaping the body. If one were to lose their entire aura, it would be equivalent to using up all the energy keeping them alive, which would be fatal. The pores or points on the body from which aura flows out from are called "Aura Nodes" (精孔) (しょうこう, Shōkō). Controlling those nodes is the first step to being a user of Nen.
Learning to use Nen is the final step in becoming a professional Hunter because most contracted jobs require the use of it as the minimum requirement. The technique has the ability to enhance the strength of physical attacks or objects depending on the quantity of aura employed and an individual's aura type, as well as allows for para-psychological abilities to exist in reality. Because one can craft just about any sort of psychic power through only using their mind, Nen is also a dangerous power unknown to the public at large. Crimes committed using Nen fall within the jurisdiction of the Nen Police, but offenders may also be targeted by the Hunters Association.
Learning Nen and Initiation
A student learning Nen trains to manually open and close their aura nodes so that they can control the flow of their aura. One typically learns this process slowly and gradually through meditation. The second method (colloquially called Initiation or Baptism) is by having one receiving an influx of aura from an experienced user that forces these nodes to open; despite how quickly it works, the method is typically frowned upon due to its danger to the student if the user is inexperienced or has malicious intent. Initiation via physically attacking another with the use of an enhanced aura typically causes permanent disability or death.
There is, however, a way to initiate that is less harmful to the student's body — depending on gently jolting open one's nodes forces the new user to learn to control their aura flow, else risk suffering severe exhaustion or death. This method is called Gehou. Once one has opened their aura nodes, he will be able to see his own aura as a shroud surrounding the body due to his nodes in his eyes being opened. Aura looks similar to steam from a kettle.
It is possible to feel the presence of aura even without being aware of its existence. It has been described as feeling like a warm, viscous fluid at rest. It has been said that powerful, refined auras produce a sensation that feels akin to needles pricking into the skin. Since every living being emits aura subconsciously, learning to sense aura is a useful skill for those tracking living things or hunting non-living things infused with aura. An experienced user of Nen can judge the location and relative strength of his opponents through reading the output of their aura.
Upon his introduction, Wing taught Killua and Gon a fake sense of Nen that focuses mostly on meditation and on one's self. This method does not require any aura and has no visible effect; however, after Gon was injured by Gido and forbidden to use Nen for two months to recover by Wing, both Gon and Killua practiced this method, and in fact made it more natural for them to use regular Nen. Given that Nen is linked to emotions and mental state, this method can be particularly useful to train Nen without aura, although normal use of technique is usually preferred.
Nen of the Flame
Nen of the Flame (燃, Nen) is sometimes used in Shingen-ryū kung fu as a precursor to learning the actual Nen. They are mental exercises akin to meditation that strengthen one's force of will. Regular practice can smooth the flow of one's aura. The Four Exercises of Nen of the Flame are as follows:
- Ten (点, Point): Focus the mind, reflect upon the self, and determine the goal.
- Zetsu (舌, Tongue): Put it into words.
- Ren (錬, Temper): Intensify your will.
- Hatsu (発, Release): Put it to action.
Nen is like any other skill, in that there are those who will learn it faster than others. Some are able to discover and learn to manipulate their aura on their own without having formally learned it. These individuals are typically known as "geniuses," "psychics," or "superhumans" to the public. This can be anything from inadvertently being able to use the basic techniques of Nen or unconsciously developing a unique Nen ability that can be used without really understanding how or why one is able to do so. Typically, geniuses of Nen are exceptional artisans in their own fields and their abilities are related as such.
Notable geniuses within the series include:
- Neon Nostrade, the fortuneteller.
- Benny Delon, the mass-murderer and blacksmith.
- Zepile, the counterfeit artist.
- Komugi, the Gungi world champion.
- Alluka Zoldyck, the wish granter.
Nen and Emotion
Although the production of aura is unconscious and constant by all living beings, it is not only life energy. Aura carries with it the desires and emotions of the one who deploys it, which is what allows for Nen to have incredible versatility to those who develop their skill at using it, and also heavily influenced by mental condition and emotional state. A basic application of this phenomenon is that one can channel their aggression or malice into their aura and deploy it towards another person (i.e. blood-lust). The antagonized will then be able to feel that blood-lust as if it were physically palpable; if unable to keep it from their own body by deploying their own Nen, he/she may be physically harmed by it.
Vows & Limitations
Being a product of the mind, Nen responds to the goals, strengths, and desires of individual users. As a result, a student of Nen can increase the overall power of an individual skill by stating a self-imposed restriction that forces even more conditions on it. For example, if one consciously decides something along the lines of "I will only use this skill on Thursdays" or "I will only use this skill against short people" and manages to abide by that rule, that particular skill will become stronger. These conditions are called "Vows" (制約, Seiyaku) or "Contracts". The stricter the Vow, the more one's own ability is strengthened. It is also implied that Vows that carry great meaning or are tied to emotional states also bring about a greater benefit. However, Vows are also considered liabilities, since breaking a Vow carries the risk of completely obliterating one's own Nen abilities.
Vows that contain some sort of punishment (e.g. "I will die if I break this rule") will strengthen the ability even further. These are called "Limitations" (誓約, Seiyaku) or penalties—covenants to oneself. An example of this is the character Kurapika, who swore on his own life not to use an ability on anyone but the Phantom Troupe. Even though a Vow adds further Limitations to using one's Nen ability, a Vow is not the primary condition for an ability's activation and acts only to enhance its power. It is also useful in retaining one's abilities when breaking a vow. When a person breaks a vow without a limitation, they risk damaging their abilities, however, when there is a limitation, this risk is removed (unless of course it is part of the limitation), at a price of one's own choosing.
Nen can be used to place a curse upon others. They are considered dangerous due to their long-lasting effects. Curses may disappear if certain conditions are met by the cursed, but they can also be removed through the use of Nen. Those who possess the ability to do so are called Exorcists (除念師, jonenshi), but are rare among Nen users. There are fewer than 10 people in the entire world whom are powerful enough to exorcise Nen curses left by the dead.
Notable Exorcists include:
Though Nen is influenced by one's mental condition and emotional state, it is difficult to judge exactly how these factors affect Nen. In certain instances, these factors may even lead to one exceeding the 100% limit cap. However, using one's powers beyond their capacity will ultimately cause strain. Potentially, this could become either a weakness or fatal to the user. Gon is an example of exceeding the 100% limit cap: after the boost, he would have died without Alluka's intervention, and even so, he reverted to a stage where he cannot use his aura. According to Ging, he was lucky to get away with only that, and if he wants more, there will be a price to pay. Nen also does not necessarily disappear following death. In fact, sometimes death can reinforce an ability's strength. If someone dies holding a deep grudge, his Nen will remain and seek out the object of his hatred.
Four Major Principles
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, 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 during sleep.
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.
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.
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.
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.
Nen and Individuality
There are six types of aura; every individual is born having one of these six different aura types. Upon learning one's own aura type, a student of Nen can set about learning to apply the technique in a unique way that suits their personality, which can develop into a unique skill. The most popular way (and the only sure-fire way seen in the series) of determining one's aura type is through Water Divination (水見式, Mizumishiki). Divination requires one to float a leaf atop a glass of water. A student of Nen will place their hands around the glass and perform Ren. The resulting effect from one's aura contacting the glass will determine a person's aura type.
- If the volume of the water changes, the user is an Enhancer.
- If the taste of the water changes, the user is a Transmuter.
- If impurities appear in the water, the user is a Conjurer.
- If the color of the water changes, the user is an Emitter.
- If the leaf moves on the water's surface, the user is a Manipulator.
- If a completely different change appears, the user is a Specialist.
It is best to base a Nen ability on one's individual aura type. Though it is possible for one to develop abilities outside of his primary aura type, one is typically less proficient at using those abilities. By creating an ability that one isn't suited for, one risks stagnating their potential by overloading their capacity for using Nen something Hisoka calls "Memory Overload". However, this is not the case with those who have absolute mastery over Nen, e.g. Biscuit Krueger and Isaac Netero. Biscuit is able to materialize several Nen masseuses (only Cookie was shown so far) that involve the mixture of Emission, Manipulation and Transmutation, and with casual ease.
Hisoka also claims that he is able to judge a person's Nen type based on their personalities. According to him, all people of one aura type are generally of the same personality type. However, he also states that this method is similar to trying to find someone's star signs or blood type just from personality analysis — it is not always correct. According to his theory:
- Enhancers are determined and simple. Most of them never lie, hide nothing, and are very straightforward in their actions or in their thinking. Their words and actions are often dominated by their feelings. They are generally very selfish and focused on their goals. This is reflected in their nen as enhancers typically rely on simple and uncomplicated hatsu techniques.
- Transmuters are whimsical and prone to deceit. Transmutation users have unique attitudes, and many are regarded as weirdos or tricksters. Often they put forth a facade while hiding the truer aspects of their personalities. Even when they don't hide their personalities they rarely reveal their true intentions. Many transmuters rely on techniques that give unique and unpredictable properties to their nen that reflects their personalities.
- Conjurers are typically high-strung or overly serious and stoic. They are often on guard as to be cautious. They are very observant and logical, rarely falling into traps. Being able to analyze things calmly is the strength of Conjurers. Many of the items that conjurers create are often used by them in a very deliberate and practical, logical fashion.
- Emitters are impatient, not detail-oriented, and quick to react in a volatile manner. Many of them are quick-tempered and hot-blooded. They resemble the Enhancers in building their impulsivity, but the difference with them, they probably tend to calm down and forget easier. Because of the nature of emission, many hatsu techniques created by emitters are primarily long range.
- Manipulators are logical people who advance at their own pace. They are all for arguments and tend to want to keep their families and loved ones safe. On the other hand, when it comes to pursuing their own goals, they do not listen to what others might have to say about it. While manipulators often use techniques that allow them to control their opponents they also prefer to use an inanimate medium to control that can be used versatility (such as smoke or pieces of paper hardened with Shu).
- Specialists are individualistic and charismatic. They will tell you anything important on them, and refrain from being close friends. But, because of their natural charisma that draws others, they are always surrounded by many people. Because specialization is unique and can have many facets, most specialists posses only one hatsu technique.
There are numerical approximations given by the manga to indicate just exactly how efficient one would be at using aura abilities that one is not born into. Starting at one's own aura type, one has the potential to be 100% efficient at using abilities based in that category alone. Then looking at the category chart (see right), one has the potential to be 80% efficient at using aura types adjacent to one's primary type, 40% efficient at the opposite or farthest category, and 60% efficient in the two remaining categories. Specialization is typically unusable for non-Specialists because it is impossible to partially use; one either can or cannot use Specialist abilities. However, Conjurers and Manipulators have 1% efficiency potential for Specialization due to being adjacent to it.
If a student increases the quantity of water in the glass during their water divination, they are an Enhancer (強化系, Kyōkakei). Enhancement is the ability to use aura to increase the natural abilities of an object or one's own body. Therefore, Enhancers are able to greatly increase their physical attack and defense and are best suited for close-ranged melee combat.
Enhancement is the most balanced category, allowing users to spread themselves evenly between offense and defense and become very strong using only simple abilities. One of the examples of more complex Enhancement abilities include enhancing one's healing factor.
Notable Enhancers include:
- Gon Freecss
- Isaac Netero
- Nobunaga Hazama
- Palm Siberia
If a student changes the taste of the water in the glass during their water divination, they are a Transmuter (変化系, Henkakei). An affinity for Transmutation means a person can change the properties of their aura to mimic something else. Similar to Emission, things created via Transmutation are pure aura. Transmutation is often mistaken with Conjuration due to their similarities. A simple way of thinking about it would be that Transmutation allows your aura to mimic properties of a substance, whereas Conjuration allows you to change your aura into actual substances. Transmuters can copy the properties of real things. For example, Killua Zoldyck uses his aura to copy the properties of electricity. Transmuters can also give their aura properties that don't necessarily mimic real things; Hisoka's "Bungee Gum" copies and combines the properties of rubber and gum, or Feitan whose aura replicates the solar sphere or Machi who transmutes her Nen into glowing threads. Transmuted substances are invisible to people unaware of the existence of Nen, and even to see transmuted aura, for a person well known to Nen, will require Gyo, or focusing the majority of Ren on one's eyes.
Notable Transmuters include:
If a student creates an object in the water in the glass during their water divination, they are a Conjurer (具現化系, Gugenkakei). Conjuration is the ability to create a physical, independent, material object out of one's aura. Once a person has mastered the conjuration of a certain object, they can conjure it and dispel it in an instant, whenever they want. Conjuration is the only way in which Nen can create things that ordinary people (unaware of Nen) can see and touch. Furthermore, objects or entities created by this technique have a subtle "independence" to them. This means that they can continue existing even if they were at a considerable distance from the Conjurer, or even if the Conjurer themselves are not aware that they have yet to be de-materialized. However the use of In can hide an object materialized from aura from experienced users of Nen.
Conjured objects can have special abilities imbued into them. For example, the Phantom Troupe bandit, Shizuku, is able to conjure a vacuum cleaner that can infinitely suck up objects, but with the condition that it can't suck up living things and things made up of Nen. Similar to Manipulation, Conjuration abilities tend to be very specific, complex, and conditional. Conditions can be imbued into conjured objects to make them stronger. Kortopi, for example, is able to materialize a perfect inanimate copy of any object or person that he touches. However, the copies of all objects generated will automatically disappear after 24 hours.
Notable Conjurers include:
If a student changes the color of the water in the glass during their water divination, they are an Emitter (放出系, Hōshutsukei). An affinity for Emission means that a user is capable of controlling the deployment of their aura while separating it from their body. Aura usually decreases in intensity very quickly when it is separated from the source body, but strong Emitters can separate their aura from their body for long-periods of time and still be able to maintain it.
Some Emission abilities (such as Shachmono Tocino's) are commonly mistaken for Conjuration abilities. The two, however, are fundamentally different. Objects created by Emitters are created solely from aura, invisible to those whom haven't learned Nen.
Notable Emitters Include:
- Leorio Paradinight
- Shachmono Tocino
- Knuckle Bine
If a student moves the leaf floating on the water in the glass during their water divination, they are a Manipulator (操作系, Sōsakei). Abilities belonging to Manipulators allow the user to control living or non-living things in a certain way (and manipulate the aura itself), the main advantage being able to 'manipulate' enemies. The degree of control is principally determined by a condition that usually puts the manipulator at risk (attaching objects on the enemy, touching the enemy in a certain way) and of course the larger the risk, the better the degree of control.
Notable Manipulators include:
- Illumi Zoldyck
- Kalluto Zoldyck
- Morel Mackernasey
- Shoot McMahon
If a student causes some other effect during their water divination, they are Specialist (特質系, Tokushitsukei). It is possible that the effect that occurs can give some insight into how they should direct their ability. Specialization is anything that doesn't belong into the other five categories. This is the vaguest Hatsu category. For example, Kurapika's Specialist ability allows him to use all Hatsu types at 100% efficiency. Chrollo Lucilfer's Specialist ability allows him to steal any other Nen ability (provided that the right conditions have been fulfilled). Neon Nostrade's specialization ability is unique, as it seems she uses only the abilities of Conjurer and Manipulator out of any of the other five Hatsu types. It is possible to become a Specialist later in life, although it is more likely for Manipulators or Conjurers which is why it is placed at the bottom of the chart.
Of the many possible effects that can occur during a Specialist's water divination, only one was shown so far. Neferpitou's aura for example caused the leaf on top of the water to dry out and crumble.
Notable Specialists include:
- Kurapika (Only when his eyes turn scarlet)
- Neon Nostrade
- Chrollo Lucilfer
- Alluka Zoldyck
After learning the basics, any skilled user of Nen will learn to utilize these advanced techniques. Most of them are achieved by using a combination of the basics. Most Nen users learn Ten, Zetsu, and Ren first before attempting these techniques. The Hatsu, being a Nen-user's individual skill, is often something that a Nen-user will develop gradually over a long period of time.
Gyo (凝, Focus) is an advanced application of Ren by which a Nen-user concentrates a larger than normal portion of their aura into one specific body part. Gyo increases the strength of that one body part, but leaves the rest of the body more vulnerable. Gyo is most often used in the eyes, allowing a Nen-user to see aura and things which would otherwise be hidden (e.g. Nen objects hidden by In).
In (隱, Conceal) is an advanced form of Zetsu used to almost completely conceal one's aura. However, unlike Zetsu, In does not require the user to stop their aura flow, but hides it instead, making this technique perfect for launching a sneak attack or laying traps. In can be countered by using Gyo in the eyes or through En.
En (圓, Circle) is an advanced application of Ren and Ten. In Ren, aura usually envelops only a small amount of space around the user's body. En is when one extends their Ren so that their aura extends further than normal, then uses Ten at the same time to give shape to the aura, usually a sphere. Someone using En can feel the shape and movement of anything entering their circle. The downside to this is that it is extremely tiring and draining for the Nen-user to constantly deploy so much aura. Those who master En are typically able to extend their En to a circle of a 50m radius. There are exceptions —Zeno Zoldyck, one of the most powerful assassins alive, is able to extend his En up to a radius of 300m. Kortopi's fake copies function as En , he was able to detect Squala's location from a distance of 2500 meters. Also, the Chimera Ant Neferpitou, has an irregularly shaped En and can extend a tendril of it up to 2 miles away.
Shu (周, Enfold) is an advanced application of Ten. Shu allows a user of Nen to extend their aura's envelopment onto an object, allowing them to use that object as if it were an extension of their own body. For example, one could use Shu to extend their Ten around an object, which would strengthen and protect the object like the way Ren strengthens and protects their body. This is the technique that allows Hisoka to make his solitaire cards as sharp and as hard as metal knives. Shu can be combined with other techniques, such as Ko.
Ken (堅, Fortify) is the advanced version of the basic Ren technique. Ken is a defensive technique where a Nen-user maintains a state of Gyo over their entire body, allowing them to defend against attacks from any direction without the need to use Ryu. Ken is useful as a defensive position, but is tiring to maintain. Additionally, it is not as strong as Gyo on any given part of the body, since it protects the whole body evenly. Because of that, it is used to guard when one wants to be cautious.
Ko (硬, Temper) is an enhanced version of Gyo in which all of an individual's aura is concentrated into one particular body part. It is a combination of Ten, Zetsu, Ren, Hatsu and Gyo. Zetsu is used to completely stop the flow of Nen in all other parts of the body. This makes that one body part exceptionally powerful, but leaves the rest of the body completely unprotected. This is used by some Nen-users as an offensive technique (a Ko-punch would carry all 100% of your aura with it), but it is a risky move — leaving the rest of one's body unprotected in a fight against another Nen-user is generally not a good idea. Ko results in one's aura creating a high-pitched dissonance, somewhat akin to the sound of metal being ground.
Ryu (流, Flow) is the term for real-time use of Gyo (the adjustment of aura concentration in various body parts) by a Nen-user in battle. For example, the use of Gyo to increase the amount of Nen in a fist as one strikes with it, to increase damage done; or to increase the amount of Nen in an arm as it is used to block a blow, for extra defense.
Quantification of Aura
Enhancement and Limitations
Reinforcement Nen plays a crucial part in close quarters combat. When two Nen users clash, it is possible to calculate the outcome using a simple equation. Physical strength is represented by the acronyms AP (Attack Points) and DP (Defense Points), depending on the action of the Nen user, while the proficiency in Enhancement is expressed in SP (Sense Points). The sum of these two factors indicates the value of one's offensive or defensive capabilities. For example, if an Enhancer and a Conjurer who possess equal physical strength and who have maximized Reinforcement, were to clash, and the Enhancer was the one attacking, his attack power would be expressed as
For the Conjurer, who has the same physical strength but whose proficiency in Enhancement would not exceed 60% even if maximized, his defense power would be
The equation representing the action is
Thus the Conjurer would suffer 40% of the damage even if he managed to block the attack correctly. This method is a simplification, since physical strength varies between people, and the location, environment and moment of the attack are fundamental variables in a real fight. Nen itself is much more complicated, since its power varies depending on the user's mental state. Because of this, it is possible to use a Limitation to strengthen one's will and thus one's aura, exceeding the normal limit. If in the same instance as before the Conjurer used a Limitation worth 2 MP (Mystery Points), his defense would become
As a consequence, the equation would be
In this case, the Conjurer would be able to block the Enhancer's attack without suffering any damage. However, due to the risks a Limitation and exceeding one's 100% limit pose, not all Nen users decide to resort to this method.
Force and Accuracy
If a Nen user learns to use a Nen type different from his natural one, the "Accuracy" (precision with which he can control it) and "Force" (power he can unleash) are proportional to his natural proficiency in that type. A Conjurer who has mastered Materialization at a hypothetical Level 10, he will be able to increase his ability in Emission up to Level 4; however, his actual skills in Emission would be inferior to those of a Level 4 Emitter, because a Conjurer can only use 40% of his Power and Accuracy for a Level 4 Emission Nen, whereas an Level 4 Emitter can use 100% of them even in Level 4 Emission Nen, since it is his natural category.
Knuckle Bine devised a way to convert aura in a numeric value, and use it in a system similar to the process of finding the Capacity factor of a power plant, in this case the power plant being the Nen user and the energy being the aura. The arbitrary unit of his system corresponds to the approximate amount of aura spent every second by a Nen user in battle mode (1 unit per second). However, once the fight starts, the aura consumption increases up to 6 or even 10 units per second, due to the usage of techniques like Ryu and Ken and of Hatsu abilities. The less skilled the Nen user and the more powerful the technique, the more aura is consumed this way. After assessing how much aura his opponents spend in combat every second and for how long they can keep using it, Knuckle is able to estimate three parameters of their aura:
- Maximum Aura Power or MAP (最大オーラ量 or MOP): the amount of aura stored inside the body of a Nen user. It varies for each individual and can be increased through training.
- Potential Aura Power or PAP (潜在オーラ量 or POP): the amount of aura expended. Continuing to compare this system to that of the capacity factor, this would be the Nen use'rs Nameplate capacity, the potential strength of their aura if they could use it at 100% efficiency, wasting none in the process. For instance, when Gon used an Emission attack against Knuckle, it required him to expend 4000au (aura units). Had his Actual Aura Power been the same as his Potential Aura Power, the damage done would be equivalent to an attack of 4000au; however, the actual damage done was only equivalent to an attack expending 500au. Gon's Potential Aura Power was 4000au, but his Actual Aura Power was only 500au.
- Actual Aura Power or AAP (顕在オーラ量 or AOP): the actual quantity of aura that hasn't been wasted. It corresponds to the amount of aura that can be exerted usefully. This is what determines the efficiency of the Nen user in how well they can use Nen. Going back to Gon's attack against Knuckle, his attack exerted 4000au but the force of the attack was only equivalent to 500au. Using the equation (500/4000)*100, the result shows that his Capacity Factor in that period of time was only 12.5%.
- In the manga, five characters have used Nen before it was explained to Gon and Killua: Illumi (Hunter Exam arc), Zebro (Zoldyck Family arc), Hisoka, Zushi and Wing (Heavens Arena arc).
- Aura can be filmed, but it will still remain invisible to those who cannot use Nen.
- The terms used for "Vows" and "Limitations" are homophones in Japanese (せいやく, Seiyaku).
- Kurapika is the only character who falls under two different Nen categories.
- Aura is translated as "Chi" (氣) in the Chinese edition of H × H. Chi is known as "Ki" (気) in Japanese.
- In the 2011 anime, the equation representing the power of Conditions is different from its counterpart in the manga: in fact, it is written as:
- In Japanese, the acronyms MAP, PAP and AAP were written as MOP, POP and AOP due to the katakana transcription of "Aura", which is "オーラ", or, in rōmaji, "Ōra". To preserve the original acronym, Viz excluded "aura" from them in the translation, with the "O" standing for "Output".
- Furthermore, the "P" in all three acronyms stands for "Power", but the kanji "量" actually means "volume".
- According to Hisoka, Enhancers and Transmuters have opposite personalities, and they might be attracted to each other because of it. There are several instances of this happening in the series:
- Gon and Killua: They are best friends.
- Gon and Hisoka: Hisoka is attracted to and fond of Gon, and has aided (or refrained from harming and/or killing) him on numerous occasions, although the interest is not reciprocated.
- Phinks and Feitan.
- Netero and Zeno: According to the latter, they are like "Yang" and "Yin" respectively.
- It is interesting to note that there are enmity between Transmuters and Enhancers in the series. For example, Enhancers Uvogin, Phinks and Nobunaga didn't get along well with a Hisoka, a Transmuter.
- Manipulation is the only category of Nen that none of the protagonists fall under.