A/N: I've never heard of Nen being used this way, but it seems extremely flexible and I can't imagine that it can't be used to heal as well as destroy.
Risoka sat in the corner, her fingers knitted together and lying useless on her lap, her posture still. She knew that on the outside, she was the picture of serenity. And in a way, she was serene--nothing could shake her to her core anymore. But her heart was still in turmoil as she looked at her favorite student and thought, At last, I am beginning to understand you. It isn't likely that you will live through this--but at least I can start to understand.
She could have spoken the words aloud, and it wouldn't have made a difference. Leorio was long past the point of hearing. His eyes were closed, his face a grimace of concentration, his breathing far too shallow. There was nothing she could do to call him back from this, and even if she could have she probably wouldn't have tried. Leorio had known the dangers of what he was getting into, and chosen to do it anyway. And Risoka respected that choice.
This was his test.
Leorio had been a Hunter for over a year when she first met him, and in that time he had not pursued more than the most basic of Nen training. Normally she would have considered this a sign of laziness and paid him no attention--indeed, if he had come to her seeking training she probably would have sent him away. But their meeting had been pure chance, and Risoka didn't believe in chance. What she did believe in was the old adage that when the student is ready, the teacher appears. Leorio seemed ready, and they had met. As soon as Leorio realized who she was and what she knew, he started asking questions.
Very specific questions. How to use Nen to heal--that one was obvious, and expected, that someone in pursuit of a medical license would wish to develop his Nen this way. Risoka could teach him this, and so could many others who used Nen the way she did.
How to use Nen to heal not only the body, but the wind--that was a more delicate art, difficult and rare, but one Risoka possessed. One, in fact, that she was considered the foremost practitioner of. Leorio did not want to learn it.
What Leorio wanted was to learn how to heal a soul. His questions became more specific. How to soothe grief. How to resolve conflict between differing ideals. How to heal a pain so deeply ingrained that it became part of someone's psyche, the way they knew themselves, past logic and past even emotion into essence. He had no interest in things she might have been able, with time, to teach him, like healing disorders of the mind. He wanted to heal the darkest emotions of the human soul--guilt, rage, despair, vengeance. And he refused to believe her when she said it couldn't be done.
Such things went too deep to be lifted by even the most experienced Nen healer. Especially if the individual in question had clung to the emotions, made them a part of their core--there was nothing an outsider could do in the face of that choice. Even when Leorio forced her to admit in the strictest of theoretical terms, it could be done--provided the Nen user was stronger than anyone Risoka had met or heard of--she cautioned him that it should not be done. Leorio was talking about altering a person's very soul, and it would leave that person lobotomized, different than they had been. This was something else Leorio refused to believe.
Risoka didn't understand his insistence. Years passed, and Leorio continued to study with quiet determination, devouring even her most viciously difficult lessons with a steadfast air. His sheer refusal to admit defeat keeping him going long past the level Risoka expected him to achieve, and soon she had to hide her surprise at how quickly he was learning. He took everything she had to offer, never cut himself any slack, and never gave an inch when they discussed what was and was not possible. He would learn to heal the body and soul as one, and he would learn to do it in such a way that the soul remained intact.
Risoka found his insistence bewildering, but not troubling. The years went by without Leorio's theory being tested. In fact, he did not seem particularly interested in practicing what he had learned. He used his skills when the need arose, and Risoka could tell his hesitance was not due to fear of making errors, but he didn't seek out opportunities to heal. He simply didn't feel the need. Risoka taught him nearly everything she knew about using Nen to heal, physically and mentally, and still Leorio acted like he wasn't done learning. Risoka let it be; he would tell her, by words or actions, when he was ready to move on.
The outside world did not disturb them for those years of study. They frequently would discuss what was going on in it, but only casually, as a matter of passing interest. Risoka, being a skilled Hunter with more years than she cared to admit, was rather well informed and often shared the interesting tidbits that came her way with her favorite student. Once she mentioned, not expecting much reaction, that there were rumors flying about a massive assault being carried out against the killing group known as the Spiders; several members confirmed dead, and further rumors and hints that there was an all-or-nothing battle for the life of the group taking place on some obscure island somewhere, and all of it masterminded by a single Blacklist Hunter.
Leorio's face drained of color as she spoke. He was out of the city within two hours, leaving a stunned Risoka behind and wondering if she would ever see him again.
He returned two days later, late at night. Risoka felt when he entered the city and was waiting outside his apartment by the time he got there. He was carrying an unconscious figure in his arms. One look at his face, and Risoka understood.
She tried to dissuade him. She knew it was impossible even as she tried. She reiterated that nothing like this had ever been successful before, told him truthfully that the person he carried was already starting to separate soul from body, warned him that the most likely outcome was that Leorio would become trapped in the other's death and they would both perish.
Leorio only replied that this was the test he had set for himself; that this moment was what he had set out to counteract all those years ago, and if he couldn't do it then the rest didn't matter anyway. He said it quietly and calmly, and even knowing it would kill him Risoka did not try to stop him again.
Instead she sat down to keep vigil, already grieving but also understanding. Realizing things she should have realized long, long ago. The kind of blind dedication to a goal that Leorio possessed was never the result of simple idealism. It was always something personal, and it was always deeply painful. Leorio had not been exaggerating when he told her that everything he had done since meeting her was in preparation for this. He knew, somehow, that the battle with the Spiders would come; he knew the Hunter who would engage in it. He knew him so well that he could predict the slow death of the soul she was witnessing now; he loved him so well that he would go through years of training on the chance that he could stop it. There was nothing Risoka could do to stop this, and there never had been.
So she watched, for hours, as night became day and then day in turn faded. Neither figure moved; not the pale blonde one, lying on the couch with the blue of death already creeping over his skin, and not Leorio, halfway sitting and halfway crouching over him, one hand touching his head, breathing those shallow half-breaths that were not enough to support hours. Neither of them moved and neither did Risoka, determined to be there when the breathing finally stopped. It was the least she could do for them now.
And then--and then, the blonde one gasped, like he suddenly needed to pull in all the air Leorio had not been breathing, and he sat up abruptly with the blanket Risoka had covered him with flying off. Leorio's hand fell away from his head but seized his shoulder instead, and then the two of them were staring at each other with impossibly wide eyes, staring amazed and breathless and unbelieving that they were still alive--until an uncontrollable smile started to grow on the blonde's face, and Leorio couldn't help returning it, and then a giggle escaped one of them. And the next thing she knew they were both laughing hysterically, shock and relief and euphoria and affection all mixed together, clutching each other to keep from falling off the couch and simply laughing as though there was nothing wrong, nothing in the world, and never had been.