There are 6 types of Nen in HxH.
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(Enhancement): The ability to use one's aura to increase the natural properties of an object or one's own body. It is the most balanced category in terms of attack and defense.
(Transmutation): Allows the user to alter the properties of their aura so that it mimics something real or acquires new characteristics.
(Emission): Refers to the ability to project and maintain the aura separate from the body. It is essential for ranged attacks.
(Conjuration): The ability to create a physical, independent object from one's aura. Unlike Transmutation, the conjured object can be seen by ordinary people who do not use Nen.
(Manipulation): Allows the user to control living or non-living substances. Often requires a "medium" (such as needles or mobile phones) to exert control.
(Specialization): A vague category encompassing any skill that doesn't fit into the other five. It's the rarest type and cannot be learned through conventional methods.
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Aside from specialization, all the others seem like great starting points for improving his Chi.
Standard Enhancement training, for example, involves taking a stone, enhancing it with aura and using it to destroy other stones without breaking the stone itself. This not only improves the Enhancement aspect but also enhances advanced Nen disciplines like Ko and Shu.
Ko is to coagulate all the aura into a part of the body, while Shu is to extend Nen to an object, but Ko is practically useless for him as well because Chi is not like Nen, which tries to leak all the time, but is extracted from the cells and can be emitted from any part of the body with little training.
Shu, on the other hand, is a useful training method, even though he can cover objects, like Umbra Alba, a good portion of the energy is wasted after he loses direct contact with his body.
But putting aside the advanced Nen disciplines for a moment, training in the other types of Nen is also very useful for him.
Emission and Manipulation to keep Chi outside the body while still controlling it. Conjuration opens doors to creating weapons made of Chi and Transmutation may be the most important, perhaps it can even change the inherently neutral property of Chi and give way to new aspects, such as healing and destruction.
Specialization, on the other hand, is not useful in the world of HxH. Specialization means opening up possibilities for the other 5 types of Nen or even a fusion of them, but for Chi, at least the current Chi, it is useless.
In any case, it's worthwhile to develop Chi based on Nen, that's a fact.
Regarding advanced Nen disciplines, there are still a few more left, but En is the only one that is truly useful for Ringo.
Basically, you project your aura in a circular radius to achieve the effect of "seeing" beyond the body. It's a very useful ability for Ringo, granting him a broader sensory aspect, especially against fast opponents like assassins.
Regarding Haki, Ringo also has some ideas.
Observation Haki is practically the En of the One Piece world, but it seems much more spiritual. Perhaps if he were a Psychic or Mage it would be more useful, but En seems more feasible for him than Observation Haki. Its advanced applications, like future vision, are even more useless for him since he can already see the future.
Armament Haki, on the other hand, gave him many ideas, in its initial state it's practically Ten, but its advanced application, internal destruction, seems exactly the kind of thing possible with Chi.
Sending a large amount of Chi into the target's body quickly and causing internal damage is basically the type of true damage skill with high damage output, it's definitely worth pursuing in that direction.
Lastly, Conqueror's Haki, its basis is practically to exert one's will over others and this is also more spiritual. It's unimaginable that Chi will one day reach a spiritual aspect, but for now, Conqueror's Haki is far from being achieved, let alone its advanced form.
From Dragon Ball, things like teleportation would also be difficult to achieve, besides the fact that he can already teleport, he can also fly in his nightmare form or by using evolutionary energy to acquire wings, but learning to fly with Chi will also greatly improve his control and will also be a good thing for Li.
Sure, things like the Kamehameha are purely energy emission and his Emission training is already focused on that. In fact, the only Dragon Ball technique he really finds interesting right now is the Genki Dama, if he can gather external life energy with his Chi, it can pave the way for several powerful abilities.
But all of this is theory for now, Ringo still has a lot of work to do. For the time being, he'll be working with Ten, trying to create a permanent shield around his body with a low energy cost.
Sighing, he began to release the Chi while trying to keep it around him, and it was... terrible. The Chi, after being released, seemed to want to spread freely, but Ringo could only force himself to continue, continuously extracting energy from the cells, expelling it and trying to pull it back in.
He was trying to create a cycle, the goal being to make his energy leak out and return to the cells with minimal loss, but unfortunately the results were terrible. He sighed and began to split his mind, one part sending energy out and the other pulling it in.
Finally, some progress was made, but this left him practically inert outside, all his concentration focused on two opposing tasks and still with a great loss of energy. But Ringo had his own solution, completely disconnecting from the outside world, his evolutionary energy began to work together. His mind split into three parts: one side sent Chi, another pulled it and the last tried to adapt to this new task.
Fortunately, he succeeded. He was still losing energy, still needing all his concentration, but... his Chi wrapped around his body like a layer of energy armor. It was a start.