Nine-Tailed Demon Fox's Attack

An event that occurred after the end of the Third Shinobi World War twelve years before the start of the series. Though many know it to be when Kurama — the Nine-Tails — attacked Konohagakure, only few know what truly occurred and who truly caused the calamity.

Prelude
The attack of Kurama, known only to everyone as the Nine-Tails, coincided with Kushina Uzumaki, the Nine-Tails' second jinchūriki, giving birth to Naruto on the night of October 10th. As child labor has been revealed to weaken the Four Symbols Seal as seen in the case of Kushina's predecessor, the Third Hokage Hiruzen Sarutobi took multiple precautions to have the birthing be performed in secret and outside the village's outskirts with his wife Biwako Sarutobi as midwife and a few ANBU as security. From there, with one of the most powerful and secret barriers that the village had to protect them, Kushiha's husband, the Fourth Hokage Minato Namikaze, maintains the Four Symbols Seal to hold the Nine-Tails at bay.

However, the childbirth's location was eventually discovered by Obito Uchiha, Minato's apprentice who thought to have died years prior. Making his way to the sight, his face covered in a mask to keep his identity a secret, Obito killed the ANBU and Biwako before holding the newborn Naruto at knife point to force Minato to back away from Kushina so that the seal can weaken. As Kushina pleaded with Minato to protect their child, Minato was able to snatch his Naruto away from the masked ninja as he attempted to stab him. But to his surprise, the blanket in which Naruto was wrapped in was filled with explosive tags, forcing him to use the Flying Thunder God Technique and transport himself and Naruto away from the explosion, but also away from Kushina as Obito counted on.

Taking advantage, Obito used a technique to forcibly extract the Nine-Tails from Kushina while noting that the Four Symbols Seal also carried the Flying Thunder God Technique seal as a security measure for Minato to teleport to his wife's aid any time. As the Nine-Tails finally emerged from the seal, Tobi used his Sharingan to gain control of the tailed beast and commands it to destroy Konoha. Kushina, due to her Uzumaki's famed longevity allowing her to survive the extraction, begs Tobi to stop as he orders the Nine-Tails to kill its former host first before Minato arrived in time to save her. The couple soon escaped back to Minato's secret location where he set Kushina beside Naruto before heading off to protect Konoha.

Even from a distance, several ninja include a young Itachi Uchiha could sense the Nine-Tails' power advancing as Obito, sneaked into the village in the dead of night and summoned the Nine-Tails into the village. When Hiruzen felt the Nine-Tails' familiar power and malevolence, he immediately prepared for battle prior to the informing him of the Nine-Tails' attack. He ordered every shinobi nearby to prepare to defend the village.

Climax
Minato arrived on top of the Hokage Monument, which Nine-Tails quickly noticed, and attacked him with the Tailed Beast Ball. Minato, using a space–time technique, teleported the blast away from the village. Before Minato could tell Hiruzen of what had happened to Kushina and her security, Tobi teleported to his location and tried to engage Minato, who used the Flying Thunder God Technique to teleport away from Konoha. Tobi followed suit, and after analysing his abilities, Minato asked if he was Madara Uchiha. Giving no definite answer that could reveal his true identity, Obito attacked Minato as both use their respective space–time techniques to avoid capture. During the struggle, Minato carefully threw his special kunai at Obito, which the latter allowed to phase through his head, and just as it did, Minato teleported right above his opponent, and landed a timely Rasengan on his back, severely injuring him.

A bewildered and struggling Obito tried to escape, but Minato, having placed his Flying Thunder God Technique seal on his body as well after his attack, teleported to his location, and placed another seal onto Obito, releasing the Nine-Tails from his control. Proclaiming his mentor truly deserved his title of Hokage for this feat, Obito teleported away, promising revenge in the future.

Despite no longer being under Obito's control, now motivated by its own malice towards the village responsible for being sealed in the first place, the Nine-Tails continued its rampage of Konoha. However, it was soon pushed outside of Konoha's premises by the village's shinobi. Hiruzen and other shinobi continued their attack on the beast, trying to push it back further. During this time, a young Iruka Umino was protected from the Nine-Tails by his mother as his father tried to help repel the beast. Ignoring his father's orders to leave, Iruka stayed, determined to protect his mother, but another shinobi soon took him away from the battle with his parents dying some time after. Several young shinobi were also detained from the battle (including Asuma Sarutobi and Kurenai Yūhi) so that another generation would survive the battle and continue the Will of Fire.

Minato arrived at the village again, and was horrified at the destruction. Just as the Nine-Tails was about to fire another Tailed Beast Ball at Konoha, Minato summoned Gamabunta to hold off the Nine-Tails for the moment. Minato then managed to teleport himself and the beast away from the village, letting the blast detonate without any casualties. He approached Kushina, who used her own chakra to constrain the Nine-Tails with the to reseal the beast within her with the process killing them both. However, for various reasons including that death would not stop the Nine-Tails, not wanting his wife to die, and to prepare for the masked ninja's return, Minato devised a plan to seal the Yin half of the Nine-Tails' chakra within himself using the Dead Demon Consuming Seal, sacrificing his soul in the process, so the Nine-Tails could be instead sealed within Naruto using the Eight Trigrams Sealing Style.

When Hiruzen and a few other shinobi finally caught up to Minato, they found him, Kushina, and Nine-Tails inside of a barrier. Kushina, initially against their son becoming a Jinchūriki, pleas with Minato to live and raise Naruto before being convinced that it is for their son's sake as it is for the village's. While Kushina held down the Nine-Tails with her chakra, Minato uses the Dead Demon Consuming Seal to sealed away the Nine-Tails' Yin chakra within himself to weaken the Nine-Tails, as it decreases dramatically in size, before proceeding to beginning the sealing process. Realising what Minato is up to, the Nine-Tails tries to kill Naruto to stop the sealing. However, Naruto's parents stop the Nine-Tails' claw from reaching their son, fatally wounding themselves in the process.

Nearing death, Minato gave Gerotora the key to the seal while Kushina expressed to an infant Naruto how she wanted him to live, to never forget who he was, and how she and Minato loved him. Minato jokingly told Naruto to listen to his talkative mother as he finishes sealing the fox into their son. In the process, as the Nine-Tails curses them for imprisoning it again, Minato also sealed some part of his and Kushina's chakra within Naruto to serve as both a final safeguard to prevent the Nine-Tails from totally breaking free and to assist their son in spirit during any future attempt to take full control of the Nine-Tails' chakra.

Aftermath
Since the resealing of the Nine-Tails happened far from the Konoha, only Hiruzen Sarutobi and the two shinobi that accompanied him, bore witness to Minato and Kushina's sacrifice. Hiruzen subverted all information regarding the relationship between Naruto and Minato to protect him, giving Naruto his mother's surname. With the village having suffered heavy casualties during the attack, only a few of the villagers would forgive Naruto, making no distinction between him and the Nine-Tails itself, for the Nine-Tails' actions. This was despite the fact that he was the one containing the beast, preventing it from harming the village.

Because of Minato's untimely death, and having no suitable candidates at hand at the moment, Hiruzen was forced to come out of retirement to retake his position as the current Hokage, despite his age. In later years, as Hiruzen saw the cold treatment of the villagers towards Naruto, he took steps to decree that no mention of Naruto being the Nine-Tails' jinchūriki be spoken with harsh punishment for those who break the rule. However, many of the villagers continued to ostracise Naruto indirectly, by transferring their harboured feelings of dislike for him onto their children, who too shunned him, resulting in Naruto living a lonely childhood with no friends.

Several years later, Sasuke would come to learn that his clan, tired of being marginalised by the Senju, had been planning coup d'état with his father Fugaku at its helm. This, however, never came to pass due to the clan genocide committed by Itachi Uchiha, which triggered the rise of Sasuke's campaign for vengeance on Konoha after being told by Tobi that it was the elders that had ordered it. Driven by inconsolable grief-powered rage, believing that the village and it people must pay for enjoying the peace gained for what he had lost, despite the facts that he would have most likely lost his life along with his clan and many uninvolved innocents if the Uchiha clan rebellion went through, learning that Hiruzen, someone besides a Uchiha, tried his best to help them but was spurned by the clan and his own advisers and being his protector from Danzō, along with the fact that most people are unaware of what really happened. Also, during the attack, Itachi noted that his parents were noticeably absent from the nearby vicinity. Where their whereabouts were and what they were doing is currently unknown.

In the anime, it was revealed that the fox had left behind large residual traces of its chakra during the attack. Taking advantage of this for his own agenda, Kazuma collected and sealed the Nine-Tails' chakra within his own son, Sora, turning him into a pseudo-jinchūriki.

Claims
Though the Nine-Tails had attacked many settlements regularly throughout history for no apparent reason other than those areas being breeding grounds for the darkest aspects of human nature, Jiraiya and Itachi Uchiha have speculated that Madara Uchiha was behind the attack on Konoha, citing his previous use of the beast in his legendary battle with the First Hokage, Hashirama Senju, while Minato and Kushina were personal witnesses to who they thought was the legendary ninja. But in reality, Madara had been long dead and Obito only masqueraded as Madara while constantly lying of his actual involvement in the tailed beast's rampage and that the attack was a "natural occurrence". However, meeting their son in his subconscious, as they met him on the night of the attack, the chakra apparitions of Naruto's parents warned him be wary of the Akatsuki's "masked man" Tobi. It was only during Naruto's fight with Tobi in the Fourth Shinobi World War that Kurama, having accepting the current jinchūriki as an equal, reveals that Minato sealed it in Naruto to enable his son to stop Tobi once and far all when the time came. By that moment, Tobi is revealed to be Obito.