Ootsutsuki Indra, the son of the Sage of Six Paths, is immortal. With each and every wound he received he could feel something shifting under his skin. Something different. Until one day he didn't feel the shifting but some kind of buzzing in his chakra. It made him wary to use it but he had to. And that was when he realised what the difference was. He transformed into a dragon who couldn't die of old age and that ability was passed down to his children and the rest of his descendants.
Over time they also found out that they can still take a human like form but it bears a liking to their dragon form. They have scales all over their bodies, their skin tones change and the older ones have bigger scales instead of hair.
One day Indra while on his walk in one of the many forests his brother had created in Hi no Kuni he saw one of his brother's descendants being hunted down by several Hagaromo ninja. The oldest dragon jumped in to protect the child without a thought and spewed torrents of super-heated blue fire at the enemy. The men were turned into ashes in minutes but Indra didn't dare to look away from them to be sure that they were all dead. It was only after that that he turned to the child. His hair colour was rather unique, half white half brown.
He escorted the child to the Senju compound and asked the clan head how often the clan's children get attacked and nearly killed by enemy clans. The answer angered him. It was far too many. Half of the children died out there on simple missions because they get tracked down when send alone.
After talking to his kin Indra came up with a solution for that. A village where all allied clans can live together. That union would not only allow for better training of the younger generations but also for a better way to defend the clans. Few would be bold enough to attack several clans at once.
Indra had the inheritor of his will and the secondary clan head (he needed someone to lead the ones who have yet to awaken their dragon side and make a show for the humans), Uchiha Madara build the village. The Senju, Hatake, Inuzuka, Akimichi, Yamanaka and Nara clans agreed to help with the building of the village and live in it
It was successful and other clans joined them but they also had to destroy several clans as well.
He and Madara got to meet the inheritor of Asura's will, Senju Hashirama. He is... an affectionate idiot. A capable idiot who has the Mokuton.
Indra introduced himself and his draconic brethren as the members of the Ryuken clan and decided to show the Senju the truth about the Uchihas.
Then news about the other villages worried him. And for a reason too. They had decided to go after his only non-human siblings, the Biju. It was a race against time to make sure that they are well and safe. The one who was chosen as the leader of the village had nearly given away his siblings in good will. Madara had barely managed to stop him.
The wars started. Everyone against Indra's village. They wanted the Biju, Indra's siblings. He didn't let them. He destroyed armies on his own but that took it's toll his body, not used to using so much power at once after not fighting for so long. He might as well have received a deadly wound for he died 1 week later. But he had ordered Madara to look after his siblings.
Madara didn't disappoint. He did splendid work at that. After the third war within ten years since the making of the villages they had won, Madara had made it so that there won't be anymore wars over the biju.
After that the wars ended. There was only the rivalry between the countries and the usual missions. The Biju lived in peace and lent their wisdom to Hi no Kuni's village. The dragons continued to live mostly in secret and Kaguya was never freed despite everything Zetsu tried.