As stated, Uzumaki Natsuru is an OC. Which means that he is not a real character in Naruto. Do know that he will not have any love interest, he is only here because my imagination wont let me delete him from my memory.
Naruto and Natsuru were identical twins when they were at the ages of 1-6. Naruto was held hostage at the age of 6, as a result of Natsuru trying to find him, and instead he was held hostage instead of Naruto.
They wanted someone who had no emotional support whatsoever. Naruto overheard them saying that the younger blonde was too energetic and stuff. They wanted a hostage that was quiet and someone more responsible.
Of course they were too young to understand, and focused more in rescuing one another rather than getting inspected on. Though, they couldn't catch Naruto due to him being a faster runner than them.
Natsuru never really paid any mind on training and stuff, but he trained with Naruto often. The older blonde was a tad slower than Naruto, he just wanted to protect him.
In those years of stressing out, telling himself that Natsuru was still in there waiting for him. Naruto and Natsuru had already met Kurama.
-Just so you guys know, Natsuru has the Yin of Kurama, and Naruto has the Yang.-
When Naruto finally stopped telling himself that he was to blame, he stole some weapons from jonin's and went to the same place he was held hostage. It had been half a year when it happened.
What he didn't know was that it could result in a state that could possibly kill him and his brother.
After sneaking in, Naruto found Natsuru's stall and carefully opened the metal door. Only to be greeted by two mismatched eyes. Natsuru's eyes weren't like they used to be. His spark was gone.
And the older blonde's hair was a bit longer too, going down below his shoulder level.
-Natsuru's eyes are like this, right is dark crimson red, while the sclera is black. And his left eye was the same as Naruto's. Crystal blue, and white sclera.
Yin Kurama was gone, he was absorbed by Natsuru's right eye.
Meaning that Natsuru was essentially a part of being a Bijuu at this point.
-Well- most likely his still human, but he's still half bijuu due to absorption.-
When they had finally left, some happened inside the place. Another inspection in a tantrum. Resulting in many people who were working inside dying. Naruto and Natsuru tried to calm the said inspection down,
-but Naruto had a problem with activating kurama's eyes. He thinks it only happens when he is angry or upset. So he tried to force it, also resulting in both of his eyes bleeding out.
-Natsuru's right eye also bleeds when they use it too much, like essentially in a hard fight.-
When they turned 10, they decided to separate, since they both had different paths they wanted to take. Sometimes they'd hunt villagers for more food, Naruto just attacks them with a katana[like sasuke's]and takes their soul, leaving them soulless and too rotten out in the wild.
Natsuru hunts villagers with a scythe, sinking it in their stomach then chopping them up or eating them right there, Natsuru will most likely just eat the organs and leave the body to rot. But he prefers to eat them whole.
If you're wondering what they look like when transforming to that 9 tails cloak or the time when Naruto transforms into Kurama, Naruto will look like how it looks like in the 4th ninja war.
Natsuru's is a dark neon yellow and his form will look exactly like Naruto's but dark yellow :v
Lastly, Naruto and Natsuru will stay 5'4 until they die lol, and Kakashi will be 6'1.