"Feel it," Emiya Shirou said, casually placing a pitch-black cursed seal on Senju Tobirama's arm. He even took the time to shape it into the spiral mark of a Konoha ninja.
"My chakra..." Tobirama raised a finger, attempting to activate his energy. "As expected, I can't." The moment he tried, the seal on his arm flowed through him like a warm current, locking down his chakra and making his body stiffen.
However, Senju Tobirama was a genius. He immediately understood he couldn't fight the seal's power directly and instead began to proactively guide it, fusing it with his own chakra.
"This power..." A flash of surprise crossed his face. The fusion of the natural energy within the seal and his own chakra provided a considerable boost to his strength.
He had to admit, Shirou's worry about the cursed seal leading to new conflicts was entirely reasonable. If an ordinary ninja obtained this power, their chakra could be amplified to jonin levels. With training, they could become a major asset on the battlefield.
The only trouble was, the cursed seal's power was not so easy to control. Tobirama's profound understanding of ninjutsu principles allowed him to grasp it quickly, but even he couldn't achieve perfect control.
Unfortunately, he had promised not to use it for conflict. He could only hope for peace, so he would never be forced to use this power in a desperate situation.
"Let me help you release the seal," Shirou offered, beginning to form hand seals as if he only wanted Tobirama to experience the power, not restrain him. "This superficial application of natural energy is too easily mastered. I only hope this power doesn't bring new fires of war to this world."
"Lord Emiya," Tobirama said, reaching out to stop him. "There's no need to be in such a hurry. I need to judge how long this energy can seal my brother's chakra based on the changes in the seal you've placed on me."
This ancient medical ninja was a bit too simple. Perhaps being from an era of powerful experts, he assumed the ninjas of this age were all geniuses. Natural energy was not so easy to master. Tobirama had seen his brother master Sage Mode but had been unable to sense the energy himself. He knew how precious this cursed seal was, and a fleeting sense of shame pricked him.
Power meant survival. For a ninja forged in the Warring States period, it meant having more control over the situation—from the turbulent opinions within Konoha to the hostile villages circling like wolves.
Tobirama was unwilling to give up a power that could make him stronger. He could only silently promise the man he was deceiving that he would only use this power in the most critical moments. Of course, he couldn't say that out loud. What he said was also true; he did need to judge the seal's duration.
"You and your brother really have a good relationship," Shirou said, shaking his head. Having witnessed the fraternal strife of his own era, he still seemed unable to fully grasp Tobirama's devotion. He could only remind him, "If you don't release the seal, your movements might be..."
"No need to worry." Tobirama raised his arm. The seal's energy flowed slowly, but it no longer hindered his movements. Barring anything unexpected, he would have it completely under control by the end of the day.
"I already understand its principle," he said, quickly changing the subject. "Let's apply the seal to my brother. Since he has mastered Sage Mode, he can utilize it more perfectly. He might quickly absorb it for his own use."
"I'm also worried about that," Shirou sighed, extending his finger to Hashirama's arm. A pitch-black cursed seal fell onto it and, as expected, promptly disappeared.
The natural energy was instantly absorbed. Hashirama's body, sensitive to natural energy, began converting it into senjutsu chakra, rapidly pushing him into Sage Mode.
On the hospital bed, colored markings appeared on Hashirama's face. He seemed to feel the change, a look of pain crossing his features as he murmured the first word since falling into a coma.
"Madara..."
Tobirama's face darkened. What time is it! Why is he still mumbling about Madara Uchiha? Even in a coma! That monster tried to destroy Konoha and injured you to the point of shortening your life, and you're still thinking about him!
"If nothing unexpected happens," Shirou said, letting out a sigh of relief, "the patient will wake up soon. Although the cursed seal didn't work as expected, his body automatically entered Sage Mode. The recovery from senjutsu chakra is astonishing, but it might also continue to damage his lifespan."
He added, intentionally or not, "As long as he doesn't use his chakra for a while after waking up, he can avoid greater damage. As for the previous lifespan issue, I'll have to think of a way to make up for it. Because I obtained Yang Power in my era, I'm used to using it to treat patients, so my research in other medical arts has lagged a bit."
"Thank you." The worry in Tobirama's eyes finally began to fade. It had actually worked. Emiya Shirou had saved his brother. He remembered finding Hashirama on the battlefield, so injured he fell into a coma the moment he returned to the village. The best medical ninja had been helpless. This was a favor worth remembering.
"I am truly grateful," Tobirama said again, his expression serious. He praised Shirou, "Lord Emiya, you shouldn't be so modest. Without you, there would be no medical ninjas in this world willing to heal the sick." Then, he revealed his true purpose. "My brother's life is tied to the peace of Konoha and everyone's hopes for the future. In the future, everything will depend on you, Lord Emiya."
This was Tobirama's selfish motive. He didn't want to release the Impure World Reincarnation. Resurrecting Shirou had revealed ancient secrets and granted him a cursed seal. Emiya Shirou was a treasure trove.
If Shirou couldn't solve the lifespan issue, Tobirama would have to delay, trying to extract more information before letting the soul return to the Pure Land. But this ancient medical ninja was as great as the legends claimed, selflessly wanting to solve his brother's problem. It was a perfect match. Tobirama began to carefully consider how to arrange for Shirou, to keep his identity secret while not being disrespectful.
Emiya Shirou also felt it was a perfect match. Maintaining his persona, he looked with concern at the First Hokage and reminded Tobirama, "The patient is about to wake up."
Just as he said, Hashirama frowned, and the Sage Mode markings faded. The First Hokage, who had been lying flat, suddenly shot upright as if from a terrible nightmare, shouting his best friend's name in terror.
"Madara!"