"Joining Fists…!!" is chapter 643 of the original Naruto manga.
Summary
Yin Kurama questions Minato about whether or not he intended to have his son take care of the situation for him. The fox notes that it would not easily comply with its other half simply because it was sealed within Naruto. The fox then tells Minato it was not his fault that his wife died, and Naruto became a jinchuriki. Meanwhile, Yang Kurama alerts Naruto to the current situation. Back on the battlefield, Naruto and Tobirama regroup with the others, and while Naruto explains the fact that senjutsu had been effective against their opponent, Tobirama muses to himself that Naruto's ability to work with his Flying Thunder God Technique and use of senjutsu reminded him greatly of his own teamwork with his brother. Recovering from his injuries as his opponents strategise, Obito casually noted that this world no longer held any meaning and that it was time that he continued on with the Eye of the Moon Plan. Creating an enormous tree with four opened flowers, Obito creates four Tailed Beast Balls intent on destroying the remainder of the Allied Shinobi Forces. As the shinobi scramble to deal with the situation, Tobirama noted that even if he and Minato used the Flying Thunder God Technique to teleport the attack away, they could each only carry two, only halving the threat. Calling out to his brother, Hashirama once again beseeches Madara to put their battle off so that he can deal with the situation, but the Uchiha notes that they were reincarnated and as such it would not matter if they were caught in it. He then challenges his Senju rival to charge through him if he wanted to help. One of Hashirama's remaining wood clones calls out to the Alliance to not lose their nerves and explains his strategy to them. However, Obito with the use of the chakra receivers erects a barrier, intent on trapping the shinobi with the attack. As they readjust their strategy to their new predicament, Naruto notes that he had a plan but wasn't sure it would work. He then proceeds to ask Minato to bump fists with him, connecting the two halves of Kurama. The Yang half of Kurama asks his Yin half to help him by providing him with some chakra, at which the Yin half noted that him begging himself for help was weird. As Obito — wrapped in a defensive cloak — continues to decry Minato noting that it would soon be the anniversary of Kushina Uzumaki's and Rin Nohara's deaths. Noting that it only meant that tomorrow was also his birthday, Naruto tells Obito that the world would not end because he still existed within it. Donning his Tailed Beast Mode mantle, he calls out to his father who, after noting mentally to Kushina that their son had grown up, responds emphatically.