"Kagura Senju was the first. The first to have red hair, among the brown one of the Senju clan. When his parents saw his blood red hair for the first time, they were sad and elated at the same time, they thought that their son was blessed by the gods, for he would reap lives on the battlefield and gives credit to the Senju Clan but sad that the only existence their son could hope for, was one full of bloodshed, pain and suffering. The son grew and displayed his talent. The Senju were regularly popping geniuses, it was the only way for them to keep being rivals with the Uchiha, these demons with red eyes. These geniuses were of a vast variety. Some were unequaled in Ninjutsu, others in Taijutsu, Bukitjutsu, Kenjutsu. The greatest of them all were those that could become Sages. The Senjutsu masters. They, not only got the overall strenght improvement of the nature Chakra, but they also succeeded in creating a pletora of nature Jutsu. Making them unrivalled among all of their peer.
Anyway, Kagura Senju was the first among these geniuses with a weak body but an incredible amount of talent for Fuuinjutsu. The years passed and his talent went unoticed as they were at war. Who has the time to study seals when in war. Their brethen died everyday, nobody wanted to lose time writing seals, they wanted to practice jutsus and their bodies.
One day, when he was 8 years old, he was send on a mission with his squad. There they found only an ambush were everybody bar Kagura died. Barely escaping with his life after setting his brethen on fire, to keep the clan secret, he soon rejoined the clan compound where he was acculed and ostracised by the other members of the clan. There the sadness and anger of the Senju spilled on Kagura who had to take it all.
"Why did you survive, you are the weakest. Blessing of the gods, my foot, your hair are probably what made your team stand out and the cause of their death. You should be ashamed of yourself." Wives, fathers, sisters, mothers and brothers all deversed on him their grief. After they finished, his face covered in tears and snots he gave the small things he could scavage from their corpses to the famillies of the dead, and turned back. He went out and never came back once in his life, inside the Senju Compound. To this day, it is the greatest shame of the Senju Clan.
From this day to his 15 birthday, young Kagura travelled the lands, slowly unravelling the mysteries of Fuuinjutsu, the only branch of the Chakra tree he ever loved. For to him, every other jutsu was designed with destruction, theft or domination in mind. Fuuinjutsu was so much more. It was Seals and binding, yes. But it also was creation and alteration, it was a way to bring things to the world, to make it fuller.
By his 17 birthday he had created the first storage seal, the first resistance seal, the first pressure seal.
As he travelled the lands, he soon found a young girl his age, with great understanding of kenjutsu and a body to die for. She was a princess, the daughter of the Daimyo lording the lands around. After spending some times with her, they fell in love and decided to marry with the blessing of the Daymo, eager as he was to have a Fuuinjutsu Master in his familly.
As the years went by, Kagura developped numerous Seals and one special ability. This ability gave him another sense that could perceve the world around him through Chakra. He could almost read the thoughts of people if focused enough.This ability, he named the Mind Eye of Kagura. He also created the Summoning Contract which gave him lots of prestige around the Elemental Nation. Lots of clans and Daymos wanted one tailored for themselves.
When the Senju clan heard about it, the bittereness and shame was too much for them. The parents of Kagura went into a frenzy and denounciated every one of the people who slandered their son, this fatefull day. They took control of the clan and made several new policies named, unviolable, for they would be unviolable till the end of the clan, these policies insured that every kid would be tested for their talent in every available area young and would be given help according to it. They soon relinquished their power over the clan but only after imploring their son to forgive the Senju clan and help them in their war against the Uchiha.
As the years had passed and he had seen the world for what it was, Kagura chose to accept their apologies but renouce his name. From now on, he would be called Kagura Uzumaki, for the name of the Island he now was the lord of. The Senju Clan and Kagura separated in good term even though the bitterness was a difficult pill to swallow for the Senju.
Kagura sold Summoning Contract to almost everyone bar the Uchiha. Unfortunately, they juts stole the Summoning Contract they wanted from another clan that had just payed to create one. Soon the sale finished and nobody wanted new contracts. But it didn't stop Kagura from continuing his experimentation in Fuuinjutsu. He delved into his chakra and his blood, into the intrecacies of Fuuinjutsu and how it interacted with the body.
To this day, nobody knows how he did it. But he did. He passed his Mind Eye of Kagura and affinity towards Fuuinjutsu to his sons and daughter while passing the strong regenerative ability of their mother alongside her affinity towards kenjutsu to their children. A new bloodlines was created and this only because of one extraordinary man and his wife.