(A/N: I do not own Death Note or Naruto)
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Long ago there was a killer. THey called him Kira. He was able to get his hands on a weapon called the Death Note. The notebook was able to kill people by name and face. He was defeated but, the weapon was taken. His family studied it. The land was in war so they needed the weapon. They tried to duplicate the weapon but, couldn't.
Then a new energy was discovered. It was known as Chakra. With experimenting with this Chakra they created one. A new Death Note. A duplicate.
Unfortunatly this new Death Note was not as good as the original. It required chakra to use. And to kill somebody with it more Chakra had be used than the target had in general. If any less it will only take that much chakra from the target. The names also fade if the target is not killed.
The new Kira clan decided that it was not good enough. Then they were attacked. Many were killed but, there were survivors. And the Death Note was destroyed.
The Kira clan only had these new Death Notes. Soon they created new ones. These ones are tied to their blood so only one of the Kira clan can use them. The ones that weren't were killed.
They were a powerful enemy. Only the Senju and Uchiha clan rivaled their power. Said clans notice it as well. So to get rid of such a powerful enemy they banded together and destroyed all notebooks and killed all memebers of the Kira clan.
Or so they thought...
77 year later, Hikaru Kira finds himself in the Village Hidden in the Leaves.