"Regrets" (後悔, Kōkai, Viz: Regret) is chapter 647 of the original Naruto manga.
En route to the main battlefield, the five Kage see the tree form of the Ten-Tails and wonder just what it was, which leads Tsunade to ask Katsuyu to explain exactly what was happening where its other divisions were. When Shikamaru is found to be one of the victims of the tree's attack, Sakura tries to have Katsuyu heal him remotely, but Katsuyu informs her that its clones also died due to having their chakra absorbed, leading the medical-nin and Sai to rush to her comrade's side instead. The Allied Shinobi Forces members spiral into despair, and taking advantage of the all-time-low morale, Obito declares that he would not kill those who stopped resisting, but Hashirama's wood clone reminds them not to give up because the fate Obito wanted for them was no less worse than death. Hiruzen's sentiments cause Orochimaru — who had just arrived with Suigetsu and Karin in tow — to note that pessimism was very out of character for his sensei. As Madara and Hashirama continued to fight, the Uchiha reveals that even without the full chakra of the Eight and Nine-Tails, the tree form of the Ten-Tails would bloom in approximately fifteen minutes, during which Madara planned to take Obito's place using Hashirama's senjutsu abilities. As the info is relayed to him, Hashirama's wood clone called out for a Yamanaka, and while startled, Ino responds and on the command of the First, patches him through to the Alliance. Connected, the clone passes on the recent revelation, and also tries to boost the shinobi's morale, telling them decisively to not give up. As the tree moves again to attack, a large chunk of its root is cut off by a Susanoo-clad Sasuke, who asks Naruto if he had already reached the limit of his capacity. Responding to his friend's question, Naruto once again enters both Tailed Beast Mode and Sage Mode and through Ino's technique, his feelings and memories are conveyed to everyone. Remembering his time as a child and the people he had lost along the way, Naruto notes that he did not want to have any more regrets and that the sacrifices made would not be in vain.