YamaLu

Luffato is the ship between Monkey D. Luffy and Yamato.

Canon
After failing to set sail with Ace, Yamato had been waiting for his brother, Monkey D. Luffy, to arrive at Onigashima. For this reason, Yamato chased and clashed with Luffy after finding him, ignoring his time constraints in order to talk to him, even if for just five minutes. Yamato then trusted Luffy enough to request his help in achieving Oden's dream of opening Wano's borders, and told him that Kaido was her father and then expressed a wish to be freed from Kaido and an intent to leave Wano with Luffy's crew as a means to be free and explore the sea like Oden did. Therefore, after Luffy removed the explosive handcuffs Kaido had used to imprison Yamato, the two decided they would fight Kaido together. Their trust has slowly grown and Luffy even entrusted Yamato to help them protect Momonosuke.

Luffy refers to Yamato by the nickname "Yama-o" (ヤマ男?), similar to the nicknames he uses for Trafalgar Law, Bartolomeo, and Eustass Kid. Yamato appears to not understand Luffy's use of nicknames, as evidenced by the attempt to correct Luffy with the former's actual name, as well as Ulti's name when Luffy gives her a nickname as well. When battling Kaido, Yamato openly told him that he would lose to Luffy, believing that he would return, calling him "the one that Oden was waiting for", and that after that, Yamato would go to sea with Luffy and the Straw Hats, which upsets Kaido.

Fanon
The ship has gained a noticeable following after the introduction of Yamato.