The morning mist shrouded the secluded training ground Jun'ko had chosen for their session. It was a rarely visited area, hidden among the trees on the edge of the village - perfect for practicing techniques they preferred to keep private.
"Technically," Aoi muttered, sitting on a fallen log as he leafed through one of his medical manuals, "I should rest for a few more days. But I suppose observing won't hurt."
"Oh, shut up!" Jun'ko patted his shoulder. "You're almost completely healed, and besides, you're here to make sure we don't get seriously hurt, right?"
"So," Jun'ko rubbed her hands together enthusiastically, "where do we start?"
"Your paralysis technique," Ren said, keeping his tone casual. "The one you used on Sora. That was... impressive."
Jun'ko looked surprised by the request. "Oh? Did it hit you that hard?"
"You were right to keep it a secret," Ren continued. "It's always wise to have an ace up your sleeve for emergencies."
"After...after seeing what happened to Aoi," Jun'ko glanced at their friend, "I realized I couldn't afford to be predictable. Not in this village."
Aoi looked up from his book, a slight smile curling his lips. "Your concern is appreciated, even if technically the likelihood of another fight like this is relatively low..."
'You're not the only one who feels that way,' Ren mused. 'Even though I have my own goals to achieve, I can't ignore how they try to stay close to me. Even though...' His gaze drifted into a haze for a moment. 'Even though I always have to keep my guard up. In Kirigakure, you never know when one day...'
"Do you want me to test it on you?" Jun'ko asked, interrupting his thoughts.
Ren nodded. "If you don't mind."
Jun'ko formed the seals - the same precise sequence she had used against Sora. "Kanashibari no Jutsu!"
The sensation was immediate and disorienting. It was as if every muscle in his body had suddenly turned to lead. He could still breathe and speak, but the rest of his body refused to respond to commands.
"Fascinating," Aoi commented, now fully alert. "The paralysis seems to selectively affect the voluntary muscular system while leaving autonomic functions intact..."
"Could you... teach me?" Ren asked as the technique dissipated.
A mischievous smile formed on Jun'ko's face. "Oh? The mysterious Ren wants to learn one of my techniques?" He put a finger to his chin, pretending to think about it. "Hmm... I could, but on one condition."
Ren raised an eyebrow.
"You owe me a favor," Jun'ko declared with a triumphant smile. "Any one, any time, and you can't refuse!"
"Jun'ko..." Aoi sighed, "statistically, using such a vague clause in an agreement leads to..."
"I agree," Ren interrupted, surprising them both.
Jun'ko clapped her hands enthusiastically. "Perfect! Now, the key is the Yin element. You have to clearly visualize the effect you want to achieve. In my case, I imagine invisible chains enveloping the opponent..."
For the next hour, Jun'ko explained the basics of the technique, while Aoi occasionally chimed in with technical clarifications on the nervous system and chakra meridians.
"The key," she explained as Ren practiced the sequence of seals, "is finding the right image. I use chains because they come naturally to me, but you could use something else. The important thing is that it's vivid in your mind."
'Like a chakra scalpel,' Ren thought. 'Perhaps I could use a similar image - something that blocks the pressure points of the nervous system...'
"Aoi," Ren said after completing his practice with the paralysis technique, "I noticed something during your fight with Shin."
"Oh?" Aoi looked up from his manual. "Technically, considering the variables at play..."
"Your medical technique is excellent," Ren interrupted, "but physically you are vulnerable. A medical-nin must be able to survive on the battlefield in order to heal his comrades."
"That's exactly what I always tell him!" Jun'ko interjected. "You can't spend all your time studying!"
Aoi adjusted his glasses, slightly defensive. "My studies are essential to..."
"And even more so if you are strong enough to survive to put them into practice," Ren said. "I have thought of a training plan for you."
He pulled out a small scroll where he had written down a series of exercises. "For starters, you should run every morning. But not just run - bring a backpack with weights."
"Oh!" Aoi's eyes lit up. "I could use my advanced anatomy tomes! The 'Comprehensive Treatise on Chakra Meridians' weighs at least three kilos, and if I add 'Comparative Anatomy of the Kekkei Genkai'..."
"You're already thinking about turning the training into a study session," Jun'ko chuckled. "But you know what? You should also learn the paralysis technique. Think how useful it would be to immobilize a flailing patient during emergency treatment!"
"Technically," Aoi began, "the application of a immobilization technique in a medical context would require precise chakra calibration to avoid interference with..."
"Shut up!" Jun'ko lightly hit him on the head with a scroll. "Less theory, more practice!"
As the sun began to set, the group prepared to end their training.
In the evening mist, a lone figure in an ANBU mask watched from a discreet distance, his eye covered by a patch that betrayed his identity. As silently as he had appeared, he dissolved into the growing mist.
That evening, in the safety of his room, Ren pulled his notebook from the containment scroll. By the light of a candle, he began to write:
'Need to create a personal laboratory. Medical knowledge from my previous life could be used to synthesize medicine not yet developed in this world. Points to consider:
- Hidden location
- Basic chemical synthesis equipment
- Protection seals
- Ventilation system for toxic fumes
- Consult Tatsumi-sensei on containment seals for hazardous substances.'
He paused, thinking. 'I could also develop specific antidotes for the most common poisons in Kirigakure. Knowledge is power, but only if you have the means to apply it.'
As the night Mist enveloped the village, Ren carefully placed the notebook back into his scroll. His knowledge from his previous life was like seeds planted in fertile soil—he just had to be patient and careful in cultivating them.