Luffy and Yamato are allies united by their desire to remove Kaido from Wano and open up the country's borders to the world, a dream desired by the late Kozuki Oden. Yamato had known of Luffy for some years prior to meeting him, as he had met his brother, Portgas D. Ace. Although Luffy was initially hostile, he quickly came to trust Yamato and accepted him as an ally. The two, along with other members of the Ninja-Pirate-Mink-Samurai alliance helped liberate Wano.Whilst Luffy had no idea who Yamato was, Yamato knew of Luffy and had developed a huge interest in him after hearing Ace's stories. He sees Luffy as his chance to sail the world like his hero, Kozuki Oden, had also done and believes that Luffy is destined to, not only liberate Wano, but to change the world as foretold by Oden in his journal. As a result, especially upon hearing the death of Ace, Yamato desperately awaited Luffy's arrival on Wano and immediately joined his side against his own father, Kaido, once he finally appeared.Luffy was initially wary of Yamato. Though he saved him from Ulti, and he could not detect any hostility from him, he nonetheless became agitated due to the urgency of why he was on Onigashima. This resulted in the two clashing with Yamato trying to tame Luffy. Eventually, Luffy gave in and chose to listen to what Yamato had to say. Upon discovering his intense admiration for Kozuki Oden, someone Luffy had come to respect, and the fact he was willing to form an alliance, Luffy happily accepted him as an ally to defeat Kaido, and the two stormed the castle together. Luffy was also initially confused as to why Yamato called himself the son of Kaido but after Yamato explained that he chose to become a man due to his idol Kozuki Oden being a man, Luffy quickly accepted it and started to refer to Yamato as male.The two also share a sense of respect for each other. Yamato quickly accepted Luffy to lead the charge and would listen to his order to save Momonosuke. Luffy even vouched for Yamato to his allies as well. When Yamato explained to Luffy how his explosive handcuffs stops him from leaving Wano, Luffy chose to remove them for him so he could be free at last. When Yamato faced his own father, Kaido, on the roof of Onigashima, he proudly declared to him that Luffy was the man Kozuki Oden was waiting for and that he will defeat him. He engaged his father in a fierce battle on the roof until Luffy returned and when Kaido defeated Luffy yet again, Yamato resolved to face death by his side. After Luffy finally defeated Kaido using Gear 5 and passed out from exhaustion, Yamato caught him and praised him for his actions. After Kaido's defeat, according to Wano's prayer customs, he did not eat or bathe until Luffy woke up. Even though he greatly desired to join Luffy's crew and had explicitly stated he would, he changed his mind after the Admiral Ryokugyu attacked Wano. When he saw that it was Shanks' Haki that drove off the Admiral, he realized that Wano needed someone to protect it from future invaders. He told Luffy that like him, he too could not adventure freely if he had worries at the back of his mind and he could not turn his back on Wano's people. Though Luffy seemed disappointed he accepted his decision and left Momo and Wano in Yamato's hands. Before Luffy departed Wano, he told Yamato, Momo and Kin'emon that should they ever decide to be pirates he would come for them immediately, much to Yamato's delight.
