The battle of the Onigashima has finally concluded with Luffy’s victory over Kaido. The Alliance members celebrated the news. Yamato met the rest of the Straw Hat Pirates for the first time and reiterated that she will join the crew.
Yamato was Kaido’s prisoner all her life. Her only straw in life was Oden’s notes, and later Ace to reinforce her clinging to the notes, while also giving her a time to wait for: Ace’s return or Luffy’s arrival.
As a daughter of a Yanko, surely Yamato is a formidable fighter. Can you imagine the strenght of the Straw Hats Crew with her addition?
The Roof Piece between Yamato and Kaido is also deliberate by Oda to symbolize where Yamato is standing in term of strenght (on Monster Trio level and not in Brook-Franky-Robin level).
I believe Yamato and Carrot will both join, and instead of Monster Trio (Luffy, Zoro, Sanji), Weak Trio (Nami, Usopp, Chopper), and Adult Trio (Robin, Franky, Brook), we are going to get Monster Quartet (+Yamato), Weak Quartet (+Carrot), and Adult Quartet (+Jinbe).