The Secret Origin of the Ultimate Tag Team!!

Summary
The two jinchūriki's progress to the battlefield is barred by A and Tsunade. Despite Naruto's attempts to press on, the Raikage proves able to keep up with Naruto even while in the Nine-Tails Chakra Mode. Tsunade, who noted that it was actually the opposite — a miracle that Naruto could keep up with the person who held the title as the fastest shinobi alive since the death of Konoha's Yellow Flash — also stated that though she was the Hokage, she could not act independent of the Allied Shinobi Forces. Tsunade is shocked when A declares that he would kill both Naruto and B, if it came down to it, but resolved to kill Naruto at that moment because B, being a perfect jinchūriki, held greater military worth than Naruto. As A moved in to attack Naruto once again, his punch is deflected by B who had transformed his arm into that of the Eight-Tails. First-bumping his brother afterwards, the two remember the story that led up to B becoming A's brother, the many missions they went on, the advice given to A by his cousin, his subsequent death and B becoming the new jinchūriki of the Eight-Tails, and their encounter with the then thought to be Saviour of this World: Minato Namikaze, and the words he imparted to them.

Credits
es:Historia Secreta: El Equipo más Poderoso Nieznana historia najlepszego duetu