The Hidden Heart (裏の心, Ura no Kokoro) is chapter 660 of the Naruto manga.
As the two targeted jinchūriki continue to struggle against their restraints, Naruto attempts to withdraw the Tailed Beast Mode, but finds that he cannot suppress Kurama's chakra as Madara deemed his efforts futile. The White Zetsu Army clone inquires as to why Madara did not go after Shukaku first. Readjusting his strategy after contemplating his minion's words, Madara turns his focus on the One-Tail. Intercepting Madara's assault, however, Gaara creates two enormous sand-hands to help stop the chain from dragging the tanuki into the Demonic Statue of the Outer Path. Declaring that he would not let Madara have the beast, Shukaku is shocked by the Kazekage's actions; which causes the beast to remember the time when it was sealed within Gaara as a child and its declaration to prey upon his mind, should he ever fall into deep sleep. As the memories came pouring in, Shukaku also remembers the words of his previous jinchūriki: the priest who had foretold the beast of the day someone would come who would cause the beast to understand the words which were carved into his own hands: "heart" and "acceptance". This lead Shukaku to notice that the kanji for the word "love" (which was craved on Gaara's forehead) was actually a combination for the kanji for "acceptance" and "heart". As the White Zetsu Army clone decries Gaara's actions — having protected the creature which caused him to suffer for so long, and also that Gaara won't die even if Shukaku is sealed in the Demonic Statue — Madara equips his Susanoo and launches one of its swords at Gaara. As the sword hurtles towards Gaara, Shukaku intercepts it, declaring that it prided itself on its Absolute Defence after all. Manipulating the sword to boomerang across the battlefield, Madara is able to break the section of the chain Gaara held and reconnect it to the beast all while sending the sword directly at Gaara whose automatic defence protects him against the attack, but he is still knocked down. Telling the young man not to overdo it, Gaara notes that because he was no longer a jinchūriki, he could stay up as late as he wanted, as Shukaku's equal. As the beasts get dragged in, B severs one of his own tentacles, while Kurama calls out to Gaara to ask a favour. Naruto is then ejected from his Tailed Beast Mode shroud. Gaara calls out to Naruto, who begins to fall to the ground.