With Uchiha Shinji's current mastery of medical ninjutsu, unraveling the secrets of the 'Marks' wasn't particularly difficult.
After all, at its core, the 'Marks' were an extreme secret technique within the 'Breathing Technique' that pushed the body to its limits, overdrawing life force.
But nothing is absolute!
Take Kai, for example, who opened the 'Eight Gates Release.' By unlocking the final 'Gate of Death,' he could burn his body and will as fuel, unleashing power close to Six Paths-level.
Yet for true Six Paths-level beings, a technique like the 'Eight Gates Release' had limited use. They already had complete mastery over their bodies, every move and technique equivalent to opening the 'Gate of Death,' and their robust physiques and wills could withstand such strain. Thus, they could use techniques on the level of the 'Eight Gates Release' without any cost.
The same logic applied.
For ordinary swordsmen, activating 'Marks' meant trading life force for power. But for a 'monster' like Shion with her extraordinary physique, the life force consumed by 'Marks' was nowhere near enough to truly threaten her life.
So, Shinji suspected that if Shion did activate 'Marks,' they would likely only appear when she fully unleashed the 'Breathing Technique.' In her normal state, her body probably wouldn't show any marks.
With a new goal in sight, Shion was brimming with enthusiasm.
Especially after learning that, compared to others, she was essentially cheating in mastering the 'Breathing Technique,' her motivation soared.
During the lunch break, Tsunade visited the Shinobi Academy again.
Thanks to past experiences, the students knew what was coming. All eyes turned to Yakumo and Shinji, accompanied by a buzz of whispers.
"Another mission?"
"I heard Yakumo and Shinji have already completed three S-rank missions!"
"So jealous!"
Hearing the chatter around him, Sasuke felt a flicker of anticipation rise within him.
That morning, he had just told Kakashi he wanted to take on missions. Now, with Tsunade showing up at the academy by noon, he was convinced that this time, no matter what, they'd include him, a Mangekyo Uchiha.
But to his surprise, Tsunade only called for Yakumo and Shinji.
Of course.
Tsunade's true target was Yakumo alone. Bringing Shinji along was purely at the insistence of the advisory elders, and since Shinji had always performed competently without dragging the team down, even she couldn't refuse the elders' request.
After all, politics often boiled down to compromise and balance.
After briefly explaining the mission, Tsunade instructed Yakumo and Shinji, "You two, go prepare. We leave in one hour!"
"Yes!"
Yakumo and Shinji nodded in unison.
Learning that this mission was to hunt down the 'Upper Moon Two' in the Land of Iron, with teams from the Hidden Stone and Hidden Cloud Villages also dispatched, Shinji was mildly surprised.
He mused to himself, Looks like after escaping with that secret technique last time, Upper Moon Two's condition has deteriorated badly. Everyone sees it as an easy target now!
Upper Moon Two was originally someone Shinji had kept alive for testing. If another village captured it, that would be a hassle. So, he prepared to use his dojutsu power, 'Izanami no Mikoto,' without sparing any effort, to optimize the Type-3 aging potion quickly. His goal was to find Upper Moon Two before the other villages, complete the testing, and eliminate the threat cleanly.
Yakumo's mindset was much simpler: as long as it involved eliminating the demons' invading the shinobi world, she would give it her all!
Watching Shinji, Yakumo, and Tsunade leave the academy, Sasuke clenched his teeth so hard they nearly cracked, thinking, Damn it! I've awakened the Mangekyo Sharingan! Why won't they let me join the mission!
One hour later.
Tsunade's squad assembled.
Unlike last time, the team now included Jiraiya, making the lineup even more formidable.
No one noticed that the Shinji in the squad wasn't the real one but a shadow clone.
The reason Shinji could consistently fool everyone, even Neji with his Byakugan and Yakumo with her Koryugan, was due to a small trick.
It was simple, really.
A perfectly executed shadow clone was indistinguishable even to dojutsu. Most shinobi identified shadow clones through experience or familiarity with the target.
For instance, Neji and Yakumo, with their dojutsu's x-ray-like vision, could see the total chakra in someone's body. Since the 'Shadow Clone Technique' splits chakra evenly between the user and the clone, a dojutsu user familiar with the target could judge whether the technique was used by checking the chakra volume.
Shinji had countered this by using a refined sealing technique he developed to seal roughly half his chakra at all times. To others, the chakra levels of his shadow clone and his sealed-state real body were nearly identical, raising no suspicion.
After sending his shadow clone off with Tsunade's squad, Shinji's real body headed to his secret laboratory to begin optimizing the Type-3 aging potion.
As before, having already determined the general direction for optimization, Shinji laid out all the necessary materials and equipment on the lab table.
He then arranged the formulas in order and activated 'Izanami no Mikoto.'
Soon, the branches of fate appeared once more!
In the vision of his Eternal Mangekyo Sharingan, overlapping images of possible futures unfolded, most of which showed failed attempts at concocting the potion.
Clearly.
After reaching the Type-3 aging potion, further optimization was incredibly difficult. Even with the collective efforts of the potion team, developing Type-4 was a formidable challenge.
Suddenly, Shinji's eyes lit up. Among the countless failed branches of fate, he finally found one successful path.
He memorized the formula number for that successful branch and continued peering into other possible futures.
Moments later, he shook his head in discomfort, forced to stop 'Izanami no Mikoto' as intense dizziness overwhelmed him.
"Over seven thousand trials, and it barely succeeded once…"
Shinji's face darkened.
This was partly due to the heavy toll on his dojutsu and partly because he had underestimated the difficulty of refining the potion.
Fortunately, there was at least one success!
After resting briefly to recover some strength, he located the formula number and began recreating the successful potion from that branch of fate.