A slight mistake leads Naruto to create a new jutsu, but what use would a single jutsu without real offensive effects have? Enough to change the whole game.
"Alright! I think I got it..."
Our protagonist was sitting in a small clearing, the stars twinkling on the sky above. Naruto had just stolen the Forbidden Scroll, like his sensei Mizuki had told him to, and was learning the first jutsu on the scroll, the kage bunshin.
"Lets see, do the cross hand-seal, imagine the source of the clones body, gather the needed chakra and shape it into a perfect copy of yourself."
Naruto held up his hands in the cross shape required, gathered the chakra and used himself as the source of the copy, then he tried copying himself as perfect as possible. Starting with the bones, then forming the organs followed by creating muscles and skin, and lastly creating the blood.
"Kage Bunshin no Jutsu!"
With an eruption of bright blue chakra he found himself surrounded by two hundred clones.
Now, most would say that a kage bunshin is a perfect copy of the user, but in truth you simply shaped chakra to look like yourself, made it solid and you were good to go, however Naruto had build the clones not just as visual copies of himself, but rather had copied the physical aspects as well as the mental ones.
A kage bunshin is meant to give its creator all experience it gained during its life upon being dispelled, however Naruto had inadvertently created clones that wouldn't just give him mental feedback, but clones that would give him physical feedback as well, ignoring all injuries of course. Having created two hundred of them, he placed a great strain on his chakrasystem, even though his chakralevels are already those of a kage-rank shinobi, doing so had however created the same strain on the chakrasystems of his clones, his chakralevel and that of his clones now only as high as that of a gennin, however, unknown to Naruto, the Kyuubi was busy healing his chakrasystem increasing it in size and was unintentionally also doing the same with all the clones.
"Feh, what does that boy think he's doing? Throwing around his chakra like that?"
Unknown to most, the Kyuubi wasn't just a being of malice, but rather a Chakraconstruct with a rather developed mind, capable of thinking, speaking and feeling just like a human. Over the years the Kyuubi came to a conclusion, Naruto was not responsible for the sealing and had, in fact, suffered from it far more then the Kyuubi had. He would in fact have died long ago from malnourishment if not for his hidden furry, who had taken pity on him and used all available chakra to heal the wounds from the beatings and had used Yin-Yang-Release to create the necessary nutrients for the boys growth, which had the side-effects of boosting said boys chakracapacity enormously beyond even the hokage, the leader of the village.
But now it had healed the strain on the chakrasystem of all the clones and increased their total chakracapacity by two percent each.
Jumping with joy, Naruto released the kage bunshins, and his chakra spiked far beyond anything that could be considered sane, now easily rivaling the mighty Nibi in sheer chakra, something his tenant took note of...
"Hoh? This is surprising, I wonder what he just did. Oh. Ooh."
It was enough to make even the great Kyuubi blink in astonishment, and anyone that has the gall to say that she was speechless will be personally eaten by her. She didn't boggle at the amount of chakra Naruto had just gained, not even slightly, she was the greatest of the nine Biju, she didn't boggle. Still it was astonishing, truly worth her respect, it wasn't as if she was excited that someone had the potential to survive prolonged physical contact with her. Yeah, it totally wasn't like that...
"I'm gonna pull him in here next time he's asleep, and then we can talk, maybe he could accept me... maybe he won't hate me, I could t-train him, and... a-and p-perhaps I c-could be h-his f-friend...", she choked back a sob, "Maybe I could finally have a friend...", with that she broke down, crying to herself, all alone in her rotting cage...