"Okay, girls! Come here and let's create the shadow clones for your training!" Ren said and helped Ino create two shadow clones first because she was closer to him before he did the same for Hinata before the girls went on to practice their own stuff.
He first created the cooperation Shadow Clone technique to bypass the lower reserves the girls had. But in the previous week, he noticed something unexpected about it.
When people mention shadow clones, the first thing that comes to their mind is the Yin Aspect of the technique, the memory transfer. The girls supply the yin chakra, so they get the experience and memories.
But when a clone popped, it was not just the yin chakra that returned. The yang chakra returned too and Ren supplied the yang part of the technique.
To be frank, even Ren did not think about this when he created the technique. But, over the course of the last week where he helped the girls make clones every day, he noticed that his chakra grew a tiny bit stronger and denser despite him not actively training for it.
He delved into this mystery, and after some deep pondering, he realized that the yin chakra of the girls and the yang chakra of his within the shadow clones had a... peculiar interaction within a clone during its existence.
… Ren had just figured out how to dual cultivate.
Yeah, he almost wanted to drop dead from sheer shame.
Basically, because the yin and yang chakras in the clone came from different sources, they were reacting and affecting, constantly pushing against each other even though it was not visible in the appearance of the finalized technique. Somehow, that translated to refining each other in a very, very, very minuscule amount. Don't ask him how. He had no freaking idea.
It just worked.
He named this clone chakra refinement.
The gains were frankly so small that Ren almost did not notice. Only after six days did he find it strange that his chakra reserves slightly increased in their density and even that was because he was not actively training during this period of time.
If he had trained, he would have never realized this gimmick of his shadow clone co-op technique.
As for the reason why he called it dual cultivation... Ren's cheeks involuntarily flushed and he tried to push his sudden embarrassment down. He made some theories and even derived a training exercise based on this discovery, naming it Yin-Yang circling.
Not the most inspired name, but it aptly described what the training exercise did.
A male and a female would sit opposite each other and hold their hands while the man circled his yang chakra through the woman and the woman circled her yin chakra through the man.
The difficult part was that it also required the user to be able to create pure yang or pure yin chakra while also having another person capable of creating the opposite 'element' for it to work. And ninety-nine percent of ninjas never bothered to learn yin or yang release. These were exceedingly rare because ninjas focused heavily on elemental chakra instead.
The chances of a male and a female who were skilled enough to know how to use yang and yin release meeting each other were almost nonexistent. The chances of them doing this kind of thing for shit and giggles, just to try if it did something? It was as close to zero as it could be.
Ren was not surprised nobody figured this chakra interaction thingy out in the thousand years ninjas existed. Even he stumbled upon it by a complete coincidence.
Fortunately, Ino knew how to generate yin chakra due to her clan training and she helped Hinata with learning it for the co-op shadow clones while Ren figured out how to do the yang part while creating said technique.
During the Yin-Yang circling, the woman's Yin chakra refined the man's Yang chakra but it also fed into his Yin chakra, boosting both. And the same happened for the female, just the energies were reversed.
The energy interaction was indirect within the shadow clone so it was much weaker than Yin-Yang circling, which was several times more efficient.
Ren would say it was ten to twenty times better but he didn't have an exact number.
On the other hand, clones could do it passively but only for one energy. The person providing yin would get refined yin in return while the person providing yang would get refined yang in return. Just... the gains were much smaller.
Of course, the clone chakra refinement was basically providing a passive increase of either yin or yang while one of the users could also use the clones for training so it's not as if it did not have its uses. The increase in chakra, no matter how much smaller it was, was just a very welcome unintended side effect.
Not to mention, a person could create multiple clones... and Ren's inner gamer was already giddy at the prospect of crunching the numbers and min-maxing the shit out of it.
It's just that...
Er...
Well...
You see...
Ren noticed that this energy interaction between yin and yang chakras would work best if the male and female were connected more... closely. Yes. He was speaking about that kind of connection. Plug A into socket B kind of stuff.
It wasn't much. Really. Just around a... hundred-fold increase?
... Oh, sweet sage and his perverted chakra shenanigans. Ren felt so freaking embarrassed! He was never going to show that to the girls. He had the notebook with his 'research' locked behind a seal deep in his work desk at his apartment and that's where it shall stay!
What would his students think of him if they saw that kind of research? He felt like some sort of creep!
He didn't even want to discover that tidbit. But once he started pondering about the way the yin and yang chakra interacted, it just made sense. For the best gains, the practitioners needed to have sex while circling their Yin and Yang chakras.
It increased chakra efficiency and ensured there would be as little chakra loss during the technique. And a hundredfold increase in efficiency?
His inner gamer was screaming at Ren that he was a complete moron for not bending Hinata or Ino over the desk yet, but cooler, upper heads prevailed. He was their amazing teacher. How could he even show them that technique?
No. He was going to use the Yin-Yang circling with the girls, the version where they sat opposite each other and held hands, and take the smaller gains without coming off as a creep who wanted to have sex with them for power gains.
Hopefully, they will never find out about the dual cultivation aspect of that exercise... and he totally just raised a flag, didn't he?
No. Let's not even think about it.
Ren shook his head with a wry smile while his eyes lingered on Hinata's form for a moment too long and he involuntarily gulped. But then he noticed how her cheeks colored deep red out of a sudden, making him owlishly blink…
And flushed from mortification when he realized that a certain lower part of his was rising.
And she had her Byakugan on.
"Fuck me." Ren muttered very quietly under his nose in utter embarrassment.
Only for Hinata to blush even deeper as she glanced at him despite her Byakugan being activated, her entire face completely red.
Ren's eyes met Hinata's... when his mind supplied that Hyugas were masters at lip reading.
'God, this is embarrassing.' Ren put his head in his hands with a long whine full of suffering.
His image as a cool teacher was just ruined, wasn't it?
And his dick wasn't getting any softer no matter how much he wished it did!
Nor was Hinata's Byakugan getting deactivated for that matter.
From the corner of his eyes, he noticed Ino staring at them with a wide, cheeky, knowing grin and Ren decided that today just wasn't his day.
He needed some training in becoming more shameless.