Merging
The surface merging technique... At its core, it was the perfect spying ability. With that said, it could also become a threatening assassination tool, if used right.
Jun was the creator of this technique… And no one knew it better than him.
He vaguely remembered passing it down[1], but he didn't think anyone learned it afterward. It probably got lost with time, or collected dust in some library.
If Jun had to give it a difficulty rating, it would probably be considered an A-rank technique. In comparison to the great fireball, which was a C-rank, the surface merging technique was much harder to learn and master.
This was due to the fact that it drew heavy inspiration from Zetsu's signature technique, mayfly.
To master the technique one required tremendous chakra control, as well as expansive knowledge of the human body and it's composition. Once used, the technique would allow one's body to mimic a surface down to the molecular level.
By using this technique, one could completely merge with their surroundings, completely eliminating their presence and chakra-signature. In a merged state, the user wouldn't even require air to survive.
Recalling all of the details, Jun lifted his hand and performed a one-handed 'ram' seal. Filling all the cells in his body with chakra, Jun used the technique and slowly started to sink underground.
If someone were to see him, they'd probably think he was a ghost.
Fully concentrated, Jun allowed his entire body to submerge underground, where he started moving around.
'As I thought… This speed is way to slow. Its as fast as walking.'
Although it undoubtedly was a disadvantage, the technique more than made up for it with its advantages. Satisfied, he continued to train.
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Time seemed to fly, and soon, the sky was almost dark. Realizing how long he had spent training, Jun literally came out of a tree and landed on the ground, exhausted.
Catching his breath, he wiped off his sweat and walked back to the cabin, where Aito was waiting. Seeing him arrive, the latter jumped up with excitement.
"Aniki! I heard that you passed the exam!"
"Did you ever doubt it?"
"N-no… Anyways, congrats! Akane told me to tell you that we should go celebrate at her place, she's even prepared a feast for us!"
"Really? I mean… I won't reject her hospitality... Let's go there after I shower, hm?"
"Sure, I'll be waiting outside!"
If she was going to go out of her way to prepare dinner, saying no would be too rude. Jun decided that a little fun wouldn't be that bad.
After showering, he put on some basic clothes and left with Aito.
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[1] So here's where some plot-fixing happens. The surface merging technique is actually referred to as the 'hiding in surface technique', by the fandom. We first saw it through Orochimaru back in the forest of death, but it was never really explored, not including the few people who were listed as having it. It was never mentioned in the databooks either.
With that said, since Madara is also listed as a user in the wiki, I decided to make him the originator of the jutsu. Although you already read it, the backstory that I fabricated goes along the lines of him studying Hashirama's and Zetsu's abilities. Then, he passed it on to someone and a few people learned of it as a result. I hope it makes sense to you all!