It all began with Orochimaru's demise all those years ago. Two saviors rose from the destruction that Orochimaru had caused, and were declared heroes. The first was Uzamaki Naruto and the other was Uchiha Sasuke, who everyone had thought was on Orochimaru's side, but Naruto finally knocked some sense into him.
Well after that war, there was a time of great peace, in which the heroes were married, had children, and lived relatively peaceful lives, each of them rebuilding the village in their own way.
Naruto finally achieved his dream of being Hokage and Hyuuga Hinata got her dream of being with Naruto. They were married and they had one child, and one was enough. That child's name is Uzamaki Hyuuga Saru. He is named for the late Sarutobi, the 3rd Hokage, who Naruto felt he needed to honor with naming his child after him, which turned out to be an interesting idea, because the boy took to the name 'monkey' quickly. He turned out to look a lot like his father in most respects, even the whiskers, but got the Byakagun of his mother's family. He is now 16 and is in line to be the first blonde head of Hyuuga, which he finds to be a source of inspiration to be always improving. He also has his mother's certain shyness around certain people, but is always open to arguing for something he believes in.
Sasuke started to rebuild his clan, with his new wife, the new Mrs. Uchiha Sasuke, Sakura. They had three children, all girls. The oldest's name is Uchiha Yuri, named after a flower like her mother. She was born on the same exact day as Saru and since they were aware of it, they have always been rivals. She is an even mixture of her mother and father, brooding and dark one minute, angry or crying the next, especially around Saru. She got her Sharingan around the age of 8 and has been training to control it ever since.
Now these two children grew up around each other, nearly every day were they together, but not by their own free will. They were babysat when their parents were out on missions, or when they were old enough, spent all their time at the academy. Yuri is, and always has been very serious about her training. She is normally trained, privately, by Kakashi. And in this way she has been able to improve her Sharingan many fold in her short life. Saru on the other hand, is a little more light hearted and takes his training seriously, in his own way. The only time he is really serious about training is when he is training with his mother's side of the family, so he can become the strongest Hyuuga so his grandfather will recognize his strength and accept him as a Hyuuga.
Now this story begins right after these two children become Jounin, both at the same time, which to them is a nuisance. They have had to spend too much time together and they compete constantly, especially since they are from opposing clans. And their first mission as Jounin is together and both of them have their objections.