From a distance, Uchiha Shinji kept watch while occasionally glancing at Neji, who stood before the giant Tenseigan.
The reason Neji could siphon chakra from the giant Tenseigan without alerting the Otsutsuki branch family was simple: the amount he absorbed was negligible compared to the giant Tenseigan's vast reserves, barely a drop in the bucket, insufficient to raise suspicion.
From Shinji's perspective, it wasn't so much that Neji was absorbing chakra through resonance as it was Neji lingering near the giant Tenseigan, leveraging his Byakugan to avoid rejection and collecting the chakra it naturally emitted.
Even this tiny amount of Tenseigan chakra quickly filled Neji's body and the 'biological exoskeleton' within moments.
Returning to Shinji's side, Neji reported, "Sir, I've reached full capacity!"
Shinji shook his head. "Too little!"
Neji looked troubled. "But my body and the 'biological exoskeleton' can't store any more!"
The 'biological exoskeleton' Shinji had developed could, in fact, continue absorbing and storing chakra, but its ability to do so relied on sealing jutsu, requiring time to gradually seal and store the chakra.
For instance, the half exoskeleton in Neji would need at least a full day to fully seal the Tenseigan chakra it had already absorbed.
"We don't come here often…"
After some thought, Shinji activated Wazunagi, siphoning all the Tenseigan chakra Neji had just absorbed into his own body.
Instantly, a stream of sapphire-blue chakra flooded into Shinji.
His body couldn't store Tenseigan chakra for long, as his own chakra would attempt to assimilate it, eventually contaminating the high-purity Tenseigan chakra with his lower-grade chakra.
But he clearly had another method for storage.
He swiftly activated Susanoo Tomoshibi, manifesting a small skeletal arm before him. The Tenseigan chakra drawn from Neji via Wazunagi now gathered in the palm of Susanoo's skeletal hand.
Neji was startled. "This is!?"
"My Susanoo can serve as a vessel to store various types of chakra," Shinji explained briefly before urging, "Don't just stand there—go absorb more Tenseigan chakra!"
In the original timeline, Sasuke had used his complete Susanoo as a container during his final battle with Naruto, storing the chakra of all tailed beasts to unleash his strongest attack, the 'Arrow of Indra.'
So, while Susanoo was often a trump card for Mangekyo Uchihas, its utility was far broader than imagined.
After several trips, Shinji saw that the Tenseigan chakra held in Susanoo's skeletal hand had reached its limit and called Neji to stop.
Continuing would require a stronger form of Susanoo.
But on the moon, within the Otsutsuki branch family's protective barrier, maintaining even the skeletal arm form of Susanoo was risky. Activating a stronger Susanoo would be tantamount to declaring war on the Otsutsuki branch family.
After some effort, Shinji and Neji successfully escaped the Otsutsuki branch family's castle and left the moon.
Back in Hidden Leaf, Shinji's real body remained in the secret laboratory outside the village.
For his Eternal Mangekyo Sharingan, sustaining the skeletal arm form of Susanoo for days was no issue.
Thus, he could maintain Susanoo indefinitely, storing the Tenseigan chakra in its palm for Neji's half 'biological exoskeleton' to gradually seal and store.
This also allowed him to practice constructing Susanoo, strengthening it—a win-win.
In the Secret Laboratory Beneath Hidden Leaf Hospital.
Inspired by Shinji's idea, Tsunade's research team quickly synthesized an aging agent.
Tsunade announced loudly, "Everyone, attention! The live experiment is about to begin!"
At her words, everyone in the lab held their breath. Some watched the test subject, others monitored instrument data, and some handled the aging agent.
Everyone, including Shinji's shadow clone, awaited the moment the results would be revealed.
"Inject the agent!"
Tsunade remained far calmer than the others.
Shizune immediately operated the equipment, preparing to inject the aging agent into the test subject.
The so-called 'test subject' wasn't the demon chained in the lab's center—or rather, not entirely.
Due to demons' scarcity, even Tsunade couldn't afford to use them recklessly.
The 'test subject' was actually a severed tail of the demon. Since demon limbs disintegrated rapidly once detached, Tsunade had painstakingly created a nutrient delivery conduit between the demon and the tail, which could be severed at any moment, to ensure the tail retained the demon's rapid regeneration.
In other words, Tsunade had constructed an artificial blood vessel between the demon and its tail to maintain the tail's demonic properties.
If the tail encountered issues during testing, Tsunade could quickly sever the artificial vessel to protect the demon.
Soon, Shizune completed the procedure, successfully injecting the aging agent into the tail.
Tsunade called out, "Data!"
Yakumo, monitoring the instruments, reported, "No change in data… wait, it's changing! Cell division speed is increasing—170%… 290… 410, still rising! Cell division is accelerating rapidly; the agent is working!"
Her shout was almost unnecessary, as the tail's withered state clearly showed the aging agent's effect.
At that moment, a medical ninja monitoring the demon cried out, "The monster's values are changing too! The agent's effect is reaching the monster—its cellular tissue is starting to die off in large quantities!"
Tsunade made a snap decision. "Quick, sever the artificial vessel! Protect the 'monster'!"
"Yes!"
The medical ninja hurriedly cut the artificial vessel…