Saito was feeling tired after spending about two hours trying to control his chakra, he was hit by a wave of drowsiness and lost consciousness, His chakra was highly instable, what the others didn't know was that the Biju chakra was slowly seeping into Saito's own chakra making him enable to use his full chakra reserve.
Saito after falling unconscious was having dreams about his old life, he was back to his family living his daily life, the same old life he left behind, but the sweet dream soon turned into a nightmare with all his family members and loved ones killed one after the other, when he confronted the perpetrator it was none other than himself. And just as his malefic reflection was about to strangle him to death he woke up. His body was covered with cold sweat, his hands where shaking the visions of his family dying by his hand. But he soon calmed down that was just a dream.
He started checking out his body condition, he started trying his chakra control exercise. But as soon as he started moving his chakra he felt a certain anomaly, his chakra was somehow tainted by a foreign chakra wish could only be the Biju chakra.
Unlike normal Jinchuriki, Saito wasn't exposed t Biju chakra from a young age, and even those who were exposed to it later in life didn't directly absorb a huge chunk of foreign chakra into their bodies, Saito knew that for the moment he should try stopping the chakra from seeping into his own chakra reserves. So he called Karin over to help reinforce the seal.
Karin was shocked after checking the seal, the chakra was actually slowly corroding the seal, normally that seal should be strong enough to lock the chakra, even if it was stronger it shouldn't have been able to break the seal so for now she put a multi layered seal and gave Saito the way to unlock them. It didn't take much time after that for him to recover his control and he even managed to raise it to the next level, he found out that the Biju chakra he absorbed wasn't pure but was mixed with wood element chakra, wish explains why the seal was corroded, the wood nature chakra has an amazing property to absorb and weaken other chakra natures so when the seal came into contact with the seal it started absorbing the chakra that maintained the lock and even now the chakra was slowly breaking the seals so Saito had to find a solution, and after numerous tests he finally found out a solution, by using the absorbed natural chakra he could slowly repress the rampaging Biju chakra and slowly turn it into his own, but in order to fully counter the wood element chakra he should use multiple natural chakras at the same time, he knew that it was dangerous to mix the elements without proper preparation but he was out of options.
But he first needed to fully develop his sage modes, he created ten clones, each two where training an element, he was getting closer to learning sage arts for both fire and water nature chakra, while his main body was studying the eye he retrieved from Danzo, at first Saito was tempted to implant the eye, he knew that using it he could gain a huge boost in power but after some deep thinking he decided not to because he felt that using this eye will be against all that he stood for, he believed in his own strength and never did he look for an outside source to improve himself, he wanted to reach the top without having to rely on shortcuts, he knew that it was naïve and that if other people knew about his way of thinking they would mock his naivety but he believes that, this is his way of life, in his old and new one he always relied on hard work and it never failed him. But he knew that he could rarely get his hand on an intact sharingan and an awakened one. So he started studying it mostly using his earth sage mode, when concentrating the sensory ability on a single target one can perceive every small detail but the user will lose all perception of his surroundings, so he can't use it in combat. But after numerous tests Saito was finally able to discover the reason of the strange powers manifested by the sharingan, the eye had a complex network of chakra inside it that will develop and branch out and develop the more it is used, the chakra is fed to it directly through the optic nerves wish are on their own right linked to the brain, after looking at the records of how the Uchiha developed their Doujutsu's powers, he found out that the reason why the Sharingan users power changed depending on their emotional state, the more one uses the eyes the more power they gain but somehow the eyes are able to change that chakra into powerful Yin chakra closer in nature to the natural Yin chakra, but on the other hand the connection will also influence the brain making the user more emotionally instable, and when the user is feeling strong emotions they are amplified and the eyes will automatically absorb chakra and evolve the eyes, it is basically a symbiotic relationship where the user feeds the eyes his chakra and emotions while the eyes give the user power, with that Saito kept delving deeper into his research about Doujutsu, he knew that one of his biggest weaknesses is his inability to counter strong Doujutsu abilities, and from what he learned while reading the Uchiha secret documents, each person gains a special type of doujutsu ability when the next form called the mangekyo sharingan awakens.
While Saito was deep in his laboratory researching the sharingan. Jugo, Suigetsu and Fu where out of the village following a lead they found about the legendary swords. They did inform Saito, before leaving, who offered to go with them only to be rejected. The others knew that he only wanted to protect them but they wanted him to learn that they could handle themselves and that they can stand beside him as comrades. Saito had to give up, because he knew that he won't be always present, and that his companions where right about him trying to shield them, but he still had them take a communication seal just in case they were in trouble. So he went back to his research and training while Karin on her own right was learning from Tsunade and improving her Fuinjutsu.
The days became weeks and Saito was getting closer to reach a breakthrough in his research, he also managed to learn the two last sage modes, fire and wind. The fire sage mode made him able to increase the explosive power of his fire jutsus enabling him to create white colored flames that consumed everything they touched, he also could create an invisible natural chakra coat making him able to misdirect his opponents.
As for the wind sage mode his wind jutsus gained great sharpness far surpassing what he could achieve before, this sage was specialized in assassination, once he entered this state his chakra signal disappeared and all sound and smell disappeared rendering him practically invisible and with his increased cutting power he could decapitate a target before they could react. Now he needed to start preparing for the fusion process of the natural chakras.