The famous power system used in Hunter X Hunter, called Nen, has completely changed without most fans of the series created by Yoshihiro Togashi even noticing it. An ongoing exhibition on the mangaka's works in Roppongi, (Exhibition: Togashi Yoshihiro -PUZZLE-) displays two charts with revealing information on Nen, based on notes by Togashi himself, which introduce new, important rules to the already complex power system used in Hunter X Hunter.
One of the reasons why Hunter X Hunter is so successful is the capacity of its author to create complex systems of rules that would make any professional games designer feel ashamed. The chief example is Nen, the power system used in the series, based on a simple concept of utilization of "life energy", which then evolved into one of the most unique and detailed frameworks for special abilities to ever appear in a manga. After fans spent decades trying to understand the nuances of Nen, in order to appreciate in full the beauty of Hunter X Hunter's ultra-cerebral fights, they now realize that they may have to start from the beginning.
The two charts displayed in the Togashi exhibition in Roppongi, translated, shared, and commented on Reddit by user VeraciousCake, contain information that has never been revealed before, changing the understanding not just of how the power system works, but also of many important characters in Hunter X Hunter. The first chart shows the famous six "Nen Types", the six different types of aura that identify each person's unique affinity. However, it is now revealed that a Nen User can also fall between two of these types, and (most actually do), rather than having a singular affinity as was believed until now. The second chart, instead, introduces a new system to identify how well an individual has mastered his Nen abilities. There are now four ratings of proficiency for each Nen Type: Great, Excellent, Genius, and Ultimate.
Hunter X Hunter Has Made Important Changes To Nen And To Some Major Characters
The greatest contribution given by these charts is perhaps the clarification of the Nen types of many characters that were never openly stated in the series. Along with the new information about Types placement and ratings, however, this revolutionizes the Nen system, challenging many established assumptions. For example, Isaac Netero, the 12th Chairman of the Hunter Association and one of the strongest characters in the series, is now openly stated to be a pure Enhancer (of Ultimate level). For reference, Gon is merely at Great level, briefly reaching Ultimate during his fight with Pitou, at the cost of losing his Nen. This confirms that Netero's strongest ability, the 100-Type Guanyin Bodhisattva, was actually rooted in his weakest Nen Chart affinities, Conjuration and Manipulation. The Chimera Ant King Meruem, who defeated Netero and was always supposed to be an Enhancer too, is actually an Ultimate Emitter, something that no one expected.
The changes (or rather clarifications) introduced to the Nen System go well beyond that (especially concerning the characters' new mixed affinities), and for a full overview of them is best to consult the translations posted on Reddit, or the very useful explanation video provided by the always-reliable NewWorldReview on his YouTube channel. Nen remains one of the best, most interesting features in Hunter X Hunter, and the fact that it just got even more complicated will surely not scare fans of the series.
Sources: VeraciousCake on Reddit; NewWorldReview on YouTube.