Hiruzen had been relieved at first when the boy had claimed to be from the future. He had been worried that someone had revealed something about the burden Naruto carried or perhaps even his parentage. Instead it seemed he was just up to his normal scheming that would most likely end with "... so you have to take me out for ramen at least twice a week or the village is doomed."
Instead, he had started off about Atkatsuki and Obito Uchiha and how they would capture the chakra of all the Bijuu to control the world. This statement alone had alerted him that this conversation wasn't going to go how he had thought.
Naruto told him that Obito had become the Ten Tails Jinkuurichi and that he had a Rinnegan and that not even the Hokages could hurt him, but that his Sage Chakra could. He explained how before that he was Jiraiya's apprentice and had become a Toad Sage. He also explained that he had teamed up with the Eight Tails Jinchuuriki and learned to control the power of his Bijuu, Kurama, and that he used combined the two to make an awesome cloak.
"But that's not important. Obito made this crazy tree thing that was going to Bijuu blast everyone, but I was able to attach my chakra to everyone so that we were connected sort of like with Kage Bunshin, and then Dad was able to Hiriashin us all to safety. Then Obito started going all crazy again and started talking to himself. The next thing I knew he was covered in black stuff and there was a hole in my chest."
Naruto paused for a moment before continuing.
"I went to say goodbye to Kurama and he said that he was going to save me. That he was going to give me another chance. When I woke up I was a kid again."
Hiruzen was silent, seemingly lost in thought.
"I can prove that I'm from the future if you don't believe me." Naruto offered up. "I can show you the Rasengan or the Kage Bunshin."
Hiruzen nodded and indicated to go ahead.
Naruto immediately created a clone. He noticed that having his kid sized chakra (which was still about Jounin sized) made it far easier to use. He then created a Rasengan in his right hand, again with surprising ease.
"... You said you can talk to the Kyuubi. Can you ask him whether your trip through time was a permanent one or if you're just here momentarily to warn us of the future?" Hiruzen finally spoke.
Naruto was surprised by the question.
"I think I'm here permanently. Why?" he replied.
Hiruzen smiled sadly, "You must understand; I know that you're still Naruto, but you've essentially just told me that the little eight year old boy I knew is gone and never coming back."
"Oh... I'm sorry Jiji. I guess I didn't think about it like that." Naruto said awkwardly. "Um... about asking Kurama... I think it would be easier if I just showed you."
Naruto raised his fist toward the Hokage. "Bump my fist."
Hiruzen looked at Naruto, confused.
"I'm gonna connect our chakra and use that to bring you to the seal." Naruto explained to the old ninja.
Hiruzen hesitated for a brief moment before nodding. "Alright, but I'm going to need you to explain quite a few things after we're done talking to the Kyuubi." He then preceded to reach across his desk and touched his fist to Naruto's.
The next thing he knew he was standing in what seemed to be a large sewer. In front of him was a gigantic gate with a small paper seal in it's center. He looked down at the young beside him and then back to the gate. There was only darkness behind it. The Hokage had expected the beast to be there to greet them.
"Where is the Kyuubi?" he asked. Naruto's expression turned sad and he hesitated to answer.
"He's gone."
Hiruzen was surprised when it wasn't Naruto that answered. He turned towards the voice and gasped in surprise.
"Minato..." He then looked at the woman at the Forth's side. "Kushina..."
"He didn't escaped." Minato continued. "Kushina and I would have noticed if he had. It seems whatever technique he used to send Naruto back destroyed his chakra completely."
Hiruzen had so many questions he didn't know where to start. How were they here? Was the Kyuubi gone for good or would it regenerate? Why would it kill itself?
"Tell me everything." He ordered.
It took most of the day, but Naruto managed to give an abridged version of his career as a ninja. They were only interrupted once when Hiruzen's assistant came to check on them. He made sure to tell him to cancel the rest of his appointments for the day. Though they did make sure to break for a short meal.
"I'll write up a list tonight of any important event's that we're probably going to want to change and I'll bring it over tomorrow." Naruto stated as he stood up from the chair he had found himself during their long talk.
"Thank you, Naruto." Hiruzen nodded to the young man. "I'll see you then."
Naruto made his way to the door before turning back to the old man.
"...I know it's not same, but you're still going to be the one I come to when I need advise or when I need to complain about my day or when I want to get a bowl of ramen. I might not be the eight year old you knew anymore, but you're still my Jiji. You're the first precious person I ever had." With that he turned and made his way out of the room.
I know this is taking me forever to write, but hey, at least I'm writing. I just started a new job and it's been super exhausting. I wanted to touch briefly on the fact that it would be very sad to lose someone close to you because their future self had taken their body over. I couldn't really show it too much because Hiruzen has been a ninja and a leader for many years; he's not about to cry like a baby.
Again, feel free to point out any oopsie daisies or any annoying things you see in my fic. I welcome constructive criticism.