Hunter X Hunter has become a household name in the anime and manga industry over the years. The story is interesting, but what has caught the attention of many fans is its revolutionary power system. Nen is an amazing system that Togashi tirelessly developed in a masterful manner. While Nen is complicated as an energy system, some of its concepts remain simple, such as basic aura reserves. Aura Reserve is the capacity of a character's life energy, and it is this that allows Nen's abilities to be used. Throughout the story, some characters have shown impressive reserves of aura, or at least the narrative points out that they have immeasurable amounts of aura.

Hunter X Hunter: Age, height and birthday of each main character
How much do fans really know about the Hunter x Hunter characters? Here is the age, height and birthday of each main character.
8
Outside Netero
Beyond Netero is a mysterious figure Hunter x Hunter. He has yet to make a proper move, but he is fully involved in the current arc of the Succession competition going on in the manga. Beyond Netero is the son of the late Isaac Netero. This fact alone clearly shows that this man is an absolute monster in Nen and a natural talent.
Technically, Beyond Netero's powers haven't been revealed yet, and fans don't even know what his Nen type is. But simply by the way the Hunting Association treats him, and the fact that he's been to and from the Dark Continent, it can be seen that his Nenu reserves are definitely huge. This will become more clear as the story progresses and he could be a better character than Isaac.
7
Shaiapouf
Among the royal guards, Shaiapouf is not the strongest physically, but like the others, he has his own impressive abilities to show off. Shaiapouf is the strongest Manipulation Nen user around. Although he did not achieve an impressive battle, his reserves in aura were clearly given by his simple status as a royal guard.
Shaiapouf's aura reserves were so huge that he offered some of them to Merue after the explosion. His sacrifice for Meruem greatly increased his power, proving his tremendous reserves.
6
Menthuthuyoupi
Youpi is the brute force of the Royal Guard Hunter x Hunter. In terms of physical strength alone, it is definitely the best. He went up against Killua, Knuckle, Shoot, and Morel and was able to keep them at bay quite easily. In this battle, Youpi would even fall victim to Knuckle's Aura busting ability, Hakoware.
In theory, Knuckle can ruin someone from their aura and send them into debt by lending them his own Nen Aura. However, it was almost impossible with Youpi because his Aura reserves were too high and bankruptcy would take too long. This is the first time this ability has failed so horribly, and it canonically confirms Youpi's tremendous aura reserves.
5
Neferpita
The Chimera Ant arc introduced some of the most terrifying enemies the world has ever seen Hunter X Hunterknown as the Royal Guard. They are the loyal soldiers of Meruem, and it is widely agreed among them that Neferpitou, the first born, is the strongest. Neferpitou is incredibly versatile. She is both a fearsome fighter and one of the best healers in the entire series.
Like the other Chimera Ant Royal Guards, her nen reserves are actually terrifying, so much so that the mere sensation sent Knov into a mental shutdown that left him unable to continue his mission. Pitou's aura reserves are so large that she has proven to be one of the best En users, spreading her aura over an extremely large area. Her aura reserves technically only increased after her death. When Gon killed her, she returned with a post-mortem nen and gained an even greater supply of aura.

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4
Niece
Isaac Netero has reached the pinnacle of nen-championship in the world Hunter x Hunter after decades of intense training and hard battles. With that, of course, he is one character with immense aura reserves. Netero is a force of nature, but his training has given him such large aura reserves.
In his prime, Isaac Netero was an unstoppable force that could take down almost anyone in his path. Even in his old age, he was strong enough to stand up to Meruem. His ultimate ability, called 100-Type Guanyin Bodhisattva, requires a lot of aura to use, so much so that Killua could sense it from miles away.
Who is that character?

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3
Adult Gon
Adult Gon is the widely agreed upon name for the form Gon takes during the Chimera Ant Arc against Neferpitou. In order to achieve this form, Gon undergoes a vow to sacrifice all of his Nen in exchange for a temporary power boost to take down the Kingsguard. In this form, Gon was compared to Meru.
Gon's power was so overwhelming in this form that he was able to not only kill Neferpita, but also take on her posthumous return form, giving her a massive boost. This form essentially grants Gon all of the aura reserves he would have in his lifetime at once, and was one of the largest Nen reserves ever seen in Hunter x Hunter.
2
By Meru
Usually when we're talking about the best of the best in almost any category in the world Hunter x HunterMeruem, the main antagonist of the Chimera Ant Arc, is the one who comes out on top. Meruem's power is simply unmatched. He was able to overpower Isaac Neter, and not only that, but he was also able to survive the pink bomb. If anything, Meruem was still overpowered after the bomb, especially after absorbing Youpi and Shaiapouf's aura.
After the pink bomb, Meruem had the highest measurable aura reserves. This aura reserve could have increased even more had he lived longer. His nen-ability, Aura Synthesis, also allows him to absorb other characters' auras, giving him access to nearly infinite abilities and potential.
1
Alluka
Alluka is Killua's younger sister and was possessed by a mysterious creature brought from the dark continent known as Nanika. Nanika's powers and abilities are almost incalculable and can trump even the likes of Meruem and Isaac Netero in terms of aura reserves.
In a way, Alluka has access to infinite reserves of aura, allowing her to manipulate reality itself and make any wish come true. Her aura manifested when she healed Gon during the Chairman election arc. Even though she doesn't have proper control over her powers yet, Nanika is a monster in almost every way, and more information about her powers will be revealed to fans over time.