Shin Uchiha was deeply moved by Tsunade's words.
He had never expected Tsunade to remember that absurd dream of his.
After all, Shin Uchiha had only set himself that goal because he had a system. He knew that as long as he worked hard, he would achieve it.
Tsunade was different. She was Hashirama Senju's granddaughter, and Hashirama Senju had once been known as the "God of the Shinobi World," the man who stood at its very pinnacle.
Even Hashirama Senju had failed to escape the limits of his lifespan and died early. As his granddaughter, Tsunade could be said to know him better than anyone. How could she not understand just how difficult Shin Uchiha's goal was?
Tsunade did not know that Shin Uchiha had a system. Besides, even with one, his goal would not be easy to accomplish.
Shin Uchiha also understood that his system merely helped him evolve his Sharingan. Transforming his very existence was not something he could accomplish with his eyes alone.
He needed a body that complemented his eyes before he could sustain them. Even Madara Uchiha had chosen Nagato, who possessed the bloodline of the Uzumaki Clan, when seeking someone to transplant his Rinnegan into.
Even Nagato could only barely sustain the Rinnegan. When his close friend Yahiko died in his arms and he erupted in fury, summoning the Demonic Statue of the Outer Path, he could no longer sustain the Rinnegan and nearly had himself drained into a dried-out husk.
So Shin Uchiha could only rely on himself when it came to his body. When he had previously integrated the sage body, without Tsunade's help, his body would have been ruined even if he had survived. He would have ended up just like Nagato.
That night, since Tsunade was already pregnant, Shin