"Even if there was another child born that night, Minato wouldn't have asked any parent to sacrifice their child or even a child born on that same night who became an orphan simultaneously after losing both his or her parents as a result of Kyuubi's attack into such a harsh burden especially if he himself wasn't will to do it with his own child. Therefore he used and sacrificed his own newly born child and his own life for the ritual to seal away the Kyuubi. It was a tragic and cruel burden that broke Yondaime's heart, knowing that he lost everything he held dear all in one night, for the preservation of Konohagakure and preventing Kyuubi from doing more destruction and slaughtering than what it already had done."
Tsunade started sobbing as more tears came down her face. Hearing this story made her hate the position of Hokage all the more since she lost loved ones who were in some ways connected with the title of Hokage. Hiruzen himself couldn't help but let a few of his own tears fall from his face while retelling the horrific event in detail. He wiped away the tears that fell upon Naruto's face before he continued, "Before Minato went to battle the Kyuubi, he asked for one private moment alone with Naruto. I respected his wish, although I stayed close enough to the tent to hear what Yondaime was saying. While alone with his son in the tent, Minato allowed some of his tears he held back to fall freely, while cradling Naruto in his arms, apologizing and telling Naruto that this wasn't what he wanted for him. I remember him telling Naruto that he wanted him to grow up in a village where he could have grown and matured into a great shinobi and inherit the village's will of fire with both himself and his mother and be loved by everyone in the village not only as his honorable son but also as Namikaze Naruto.
"But Yondaime knew that wasn't to be because of the monster that attacked and ruined all of his dreams. Yondaime knew that he had to do something since it was both his duty as the Hokage and as a father to protect Konohagakure, to make sure his son had a future in the village he loved so much.
""Namikaze Naruto, my son, you'll be the hero who defeated Kyuubi No Yoko and saved Konohagakure No Sato," Minato whispered to Naruto before calling me back to explain what he wanted me to do. Yondaime made it very clear that he didn't want the villagers to know of his son's existence, at least not yet. Originally his intention was for Naruto to be regarded as the great hero who saved Konoha by sealing and imprisoning Kyuubi into him. The child's name was changed from Namikaze Naruto to Uzumaki Naruto. He was giving his mother's maiden last name in order to protect his true identity and heritage. Although I wished there was another way to bring down Kyuubi however, I knew that a severe price had to be paid to stop the creature. Naruto was to be made into a living sacrifice with his father giving up his life in order to save Konoha and all who live here."
Tsunade didn't want to hear the story any further. Her heart was breaking. It was too tragic and horrible to bear. Before she could interject and tell her former sensei to stop telling her the story, Hiruzen added, "However the situation had taken an unexpected twist after the kinjutsu was performed."
Tsunade's head shot up upon hearing what her former sensei said. He continued, "A very strong chakra made its way towards Naruto and infused itself into the boy's belly. However, this chakra wasn't red as we had anticipated. Rather, it was blue. No one knows what happened to Kyuubi after the kinjutsu was initiated, but one thing is certain…Yondaime was sealed into Naruto."
The Sannin's eyes widened in shock and absolute disbelief. She remained silent as her former sensei allowed her to process everything he told her up to now. A moment later, Sandaime went on, "No one else outside the village council besides you and a few ANBU who's been sworn to secrecy knows this. As far as the rest of the villagers know, Yondaime, his wife and child are dead, along with many others who lost their lives during the attack."
Tsunade was left speechless at everything she was hearing. It was so overwhelming both mentally and emotionally. She didn't know how much more she could handle and she knew that Hiruzen wasn't finished.
"As a result of this unexpected turn of events, the council and I realized that the situation concerning Naruto has drastically changed. With the boy having Minato sealed into his being, there's no doubt that he'll undergo certain physical and psychological changes in his development and acquire all, if not most, of everything that made Yondaime Hokage the man and shinobi he became known to be in Konoha and the rest of the shinobi world."
"You mean to say that Minato will takeover his own son's body," Tsunade asked in disbelief.
"No," Hiruzen quickly replied reassuringly, "Rather, Naruto will inherit and absorb his father's knowledge, wisdom, stamina, abilities and chakra in a gradual process as he grows up, basically becoming a born Hokage. The child will still be his own individual person, not Yondaime incarnate.
"Because of this, Naruto is in more danger than before. It would have been hard enough should we have let everyone know that Minato had a surviving child, with countless people seeking to spoil, pamper or adopt the young boy for their own intentions and possibly to get a hold on Naruto's huge inheritance. It's worst now with Yondaime sealed inside him, and if enemy villages and nations discovery this secret, one of two worst case scenarios could happen: one, they could either attempt to murder the child, or two, which is most likely, they'll try to kidnap the child and raise him to be part of their nation, thus corrupting the child and making him our enemy. Either scenarios would prove disastrous for Konoha and Naruto, and perhaps other villages and nations should they cross his path."
Sandaime took a moment to look at Naruto who was now fully awake and looking around the environment he wasn't so familiar with. Sighing, Sandaime continued, "…The truth is, I would have gladly took it upon myself to raise the child and guide his upbringing. However, my reinstatement as the Hokage heavily limits the amount of time I can spend with the boy and I can't entrust him with just anyone in the village, not even with any of the clan leaders or village elders. And the last thing we need is Naruto turning out like Orochimaru…I don't want history to repeat itself with Naruto causing him to become something perhaps worst than Orochimaru himself."
"…," Tsunade remained silent. The memory and hurt of Orochimaru's betrayal was still fresh in her mind.