"Oh man what a haul!" Xander exclaimed as he upended the box he'd bought instead of a plastic toy gun as had been his original intent. However, said toy guns were sold out by the time he had gotten there, so he had been forced to look for an alternative.
Evidently the shopkeeper had seen him at the bargain bin and after a few minutes conversing, had offered him a deal after learning he knew Giles. He had several costumes in the back, not displayed because they all had manufacturing errors, sometimes several and something had spilled on the box. Xander had shrugged at that, he wasn't entering any contests where such details would matter, so he easily agreed.
Well, to call them 'costumes' would be a bit too generous, what he'd bought was more like a box of costume accessories. Several forehead protectors with inverted or mirrored village symbols, incomplete weapon sets, wrongly colored sharingan and byakugan lenses, a ripped flak jacket (with a big stain on it)...
As he browsed his loot, he already began to imagine his character. This was something he and Jesse had done quite regularly, create fantasy characters. Though the memories of those times were bittersweet to Xander, he still enjoyed doing that and continued to do so as a way to keep Jesse alive within his heart.
Uzumaki Arashi was a jounin of the Leaf, one of the few Uzumaki to survive the destruction of Uzushiogakure, and even fewer of the Leaf Uzumaki's. Not the best fighter, Arashi was a more than decent support nin. He was proficient in the Uzumaki sealing arts, which paired very well with his advanced dual-element magnet release.
Quite similar to how Hatake Kakashi got his sharingan, so did Arashi acquire a sharingan eye. The biggest differences were that the Uchiha wasn't a close friend and Arashi did the transplant on his own, the rest of their team dead by then. Unwilling to have the implanted eye always active, or to constantly cover it up, Arashi turned to his proficiency with seals, leading to the development of the doujutsu integration seal.
As the name implied, the seal integrated the sharingan into Arashi's physical and chakra systems to the point where he was able to shut the implant off and generally use it as if born with it, with only a slightly higher chakra drain than a true Uchiha would experience. It didn't make the implant inheritable though, just controllable. Even so, the sealing technique had immediately been classified as an S-rank village secret!
Eventually Arashi had managed to unlock the mangekyou sharingan, awakening the power of amaterasu within that eye. Having gained the fire affinity through the implant and integration, he eventually created the dual-element inferno release, by combining amaterasu with his wind affinity. Arashi continued to gain strength and rose through the ranks, becoming one of Leaf's powerhouses.
This, naturally, translated into a certain level of fame, or infamy, outside the village. Eventually he was targeted by one of the very few Uchiha missing nin, who wanted his mangekyou sharingan. Wary of engaging a sharingan wielding Uzumaki in a direct battle, the missing nin had instead drawn Arashi into a trap, before entrapping him within the world of tsukuyomi.
Arashi had sacrificed his sharingan by using izanagi to break free of the illusionary world, launching an inferno release attack the moment he broke free. Without the sharingan to guide the chakra however, the attack was unstable and exploded before it was ready. While it killed the attacker, it also grievously injured Arashi.
Half-blind and crippled, Arashi used a forbidden medical seal to absorb what remained of the Uchiha's body, to heal by replacing his injured limbs and organs with the Uchiha's. He survived, due to his Uzumaki lineage, to become an Uzumaki-Uchiha hybrid, as if born from an Uzumaki and Uchiha parent.
Entirely unexpected, the original sharingan implant had been integrated well enough to trigger the awakening of an eternal mangekyou sharingan within the newly absorbed eye. A band narrowly encircled the pupil, with six tomoe orbiting further out was the eye's seal.
Arashi found he could now summon susano'o, despite only possessing a single sharingan. Xander decided that being of Uzumaki descent as well as having the eternal mangekyou sharingan would make up for the missing second sharingan.
He further imagined Arashi recreating swift release and dust release through pure training. Naturally senjutsu training couldn't be forgotten, via ancient Uzumaki/Senju training techniques. Xander then shuddered briefly as he imagined a dust release senjutsu rasenshuriken...
Moments before his death at the paw of Kyuubi, Arashi's left eye awakened a second eternal mangekyou sharingan, the surprise of which actually making him falter enough to be caught by Kyuubi.