Uzumaki Nagi was eleven years old when the destruction of Uzushiogakure happened. He already graduated from the Academy a year and a half before the distruction of Uzushiogakure. After his graduation, his first assignment was the task of helping the Uzushiogakure Barrier Specialist team to improve the security barrier seals within Uzushiogakure.
The Uzushiogakure Barrier system is unique compared to other ninja villages. The barrier consist of several different barriers integrated to be a complete barrier for Uzuhigakure. Uzushiogakure has designated walk path for visitors, the use of sensing barrier is to alert the security team of anyone passing through a different path than the designated ones. This sensing barrier is common and is even being used by Konohagakure. Beside the sensing barrier Uzushiogakure has another barrier that will be erected when the sensing barrier alert the barrier security. This barrier is a physical barrier that prevent anyone from entering the barrier.
The reason Uzushiogakure was trying to improve the barrier security is because out of good will, they provided Konohagakure their closest ally access similar to Uzushiogakure ninjas. Uzushiogakure ninjas is able to pass through alternate path where they will arrive Uzushiogakure faster due to shorter distance. Konohagakure detachment of ninjas could pass through the path when they got approval from the seal provided by Uzushiogakure. This is the reason Uzushiogakure wanted to improve the security, they wanted to fix this flaw without letting Konoha know about the changes.
Nagi contributed greatly towards this, where he redesigned the inscription of the private seals for getting access to past the barrier. The unique inscription allows the barrier central command to identify every seal user when they access the barrier. Furthermore, this also include the location they used the seal to pass the barrier. The changes to the identification seal will allow Uzushiogakure know everyone that passed through the barrier without the seal holder noticing.
After the changes is done, Uzushiogakure issued the new seal and distributed it to Konoha leaders. The changes helped Uzushiogakure greatly during the initial invasion by the combined forces of multiple ninja villages and clans.
When the attack happened, Nagi was under assignment by the elder to help in increasing the security of the Uzumaki and Yuki clan knowledge vault, where many advance and secret techniques as well as training methods of the clans are stored.
To avoid all the knowledge within the vault be in the invaders hands, Nagi went and collect every one of the paper, diagrams, scrolls and books everything within the vault and sealed it within his spatial seal. He also added a fake decoy for the invaders, where he seal the vault making it into a maze like seal. When the vault seal is reopened it will trigger an explosion of the magnitude depended on the amount of chakra the invaders used when they use brute force to break to the seal barrier.
Nagi then meet up with the elder which gave him the task and informed what he did, the elder praised his actions and told him that he need to get what he have away from Uzushiogakure. He informed Nagi about Uzufuyuki organization and for him to go there when he manage to leave the village. He also informed Nagi that although Danzo leads this invasion, there appear to be some irregularities seen. For one the land of sky is also involve in this invasion. For a country to get involved in the ninja world, plus they have no contact with them at all. The elders cannot figure out why they are involved.
The elder then asked him to join the evacuation of civilians; his first mission after the successful evacuation is to inform Konoha so that they can send reinforcement. Nagi accepted the mission.
When the evacuation was happening the Kiri and Kumogakure got more and more desperate as the longer Uzushiogakure stands the higher the chance that Konoha will get wind of the attack and the attack by them will almost definitely lead to war, a war which both of them don’t want currently. Because of this on the final days of Uzushiogakure where Nagi was already on his way to evacuate, Kiri and Kumogakure unleashes their final trump card, both of them sent a jinchuriki each. Although the jinchuriki was not able to unleash their tail beast full power as they do not have full control of them the power they unleashed was enough. The combined attack of two jinchuriki sealed the faith of Uzushiogakure, although they did not expect the attack to be that powerful. The attack did destroy the entire barrier system protecting Uzushiogakure as they intended making it easy for the alliance to overrun the remaining defenders.
Meantime the effect of the combined attack of the jinchuriki also felt by the evacuation location, to make it worse the attack actually resulted in an unexpected secondary explosion when the attack also hit the booby trap that Nagi had done. The unexpected blast wave scattered the evacuation fleet formation. The blast wave indirectly helped the evacuation fleet though as the blast wave also disrupted the blockading fleet, this in turn allowed part of the evacuation fleet to easily breakthrough the blockade.
After a few weeks in open waters drifting, the ship that Nagi was aboard manage to be found by few deep-sea fishermen from the land of woods, recognizing them as civilians that manage to avoid the horrific destruction of Uzushiogakure they assisted the damaged ship to dock at the land of woods.
It took Nagi a few days to recover from the drifting; when he was up and about he got the latest news about Uzushiogakure from the people that saved him. He was distraught by the situation, he knew that he has lost everyone he knew and cared about.
Several months passed and news arrived to him that there were rumors the Second Shinobi war may happen. Nagi was not interested at the war as he felt that it was not of his concern anymore. However, he wanted to take the advantage of the situation to blow off some of his steam towards everyone that what involved in the attack of Uzushiogakure.
He woke up from his depression and planned, he knew that if he wanted to do what he planned to do he need to cover up his identity as any action he do now with his current identity will lead to a manhunt of every Uzumaki survivors. He know that he needed a new identity and the only way to do that is to cover his Uzumaki characteristics completely without any flaw.
He knew that using simple seals or body change ninjutsu would not work if there were a sensory masters around. Sensory masters could identify the person through their chakra characteristics or even spiritual and aura presence.
It took Nagi two years of continuous research to design a seal that could completely cover his Uzumaki characteristics changing them completely. It could even elude sensory masters as well.
A year before his completion the rumors of the Second Shinobi war came true.
Nagi was almost fourteen years old when he sealed his Uzumaki characteristics and started his act of terror towards Uzushiogakure enemies. Every time he acted he wiped out every one to prevent reports about him, he made sure that the only report that his enemies received is their teams was missing in action, they lost all communication towards them or the team was wiped out without knowing what has happened to them.
Nagi was selective about his action. He never act around the same area twice. He made sure that the ones he attacked is behind the enemy lines where the defense is lacking. Every time he acted his action is swift. He utilize multiple barrier seals each have different purpose.
The first one was to create a genjutsu where it create an illusion outwards that there was nothing going on around the barrier area. The second seal barrier will seal the area preventing the ones within to exit the barrier. The third seal barrier is another illusion barrier but directed internally towards his enemies within the barrier. The final barrier is used to disrupt any communications going in and out the barrier zone preventing the call of reinforcement by the ones trapped within as well as preventing the ones outside to know something was going on. Nagi also made sure that each time he acted is within a limited half an hour timeframe to limit any variables that could have happen.
His action is swift and the effect is devastating as he always make use of the one within to immediately kill each other while he take out the stronger ones within that was not effected by his barrier illusions.
Nagi actions in that year prevented major powers like Kirigakure and Kumogakure getting any advantages in any incursion they made against the other forces. His tactics made everyone that fell victim of his wrath thinks that their enemy have a new trump card in play, it lead them to decide to fall back regroup and rethink their strategies. This allowed Konohagakure to be the major benefactor towards the end of the war. Konohas eastern front where Kiri and Kumo are located has limit their involvement in the war. In Konoha eyes, they thought Kiri and Kumo are not interested in war against Konoha. While in Kiri and Kumo eyes they always think that Konoha had a new weapon that prevented them to actually mount a proper offensive against Konoha.
In the end, it lead to the unofficial stalemate and ceasefire for a year before another major conflict arise again.
The Second Shinobi war ended abruptly just slightly more than a year of Nagi actions. Nagi has already turned sixteen that time, after the war ended Nagi decided to go to Konoha as he remembered what his elder told him before the evacuation. To complete the elder last wishes he started his slow journey to Konoha using the East-West fire route from Onsen-to the capital of Land of Hot water.
But of an info dump. My dumpling of a brain is steaming...
LOL, sorry but I have to. Its needed for the future chapters
Why would he NOT target Konoha? Angry, trained killer, young / teenage, who lost everything because of Konoha's betrayal, is targeting only other enemies and not Konoha, why?
And no, I don't think that 11 year old would care that 'it was Danzo! Not the village!' he would spread his revenge on all possible targets.
I was living but dead inside me for a few years after what has happened loosing everyone, depressed just like you or even worse than you have. During that period there is only killings, death, vengeance and hatred within me. What life is that? There is no light only darkness.
His own words form the next chapter. And like I said earlier, person who only wants revenge and kill everyone would also target Konoha, because without Konoha's approval there would not be Danzo or Root.
@Haymore Unlike cannon Sasuke who is an idiot and brain dead, Nagi is not?
Like you said 11 year old kid. What he saw was Kiri, Kumo and other forces not Konoha that attacked Uzushio. The ones that used their jinchuriki were Kiri and Kumo, not Konoha.
Its face value. His redesigned defenses worked. Danzo is null and void. He had no time to think of mastermind and Konoha involvement in it. The main reason is that the ones he saw that practically nuked Uzushio were Kiri and Kumo, not Konoha.