Nico Robin joins the Straw Hats. This is the last episode of the Arabasta Arc. The scenes with Pell are anime-exclusive. Unlike the anime, after Robin joins the crew, it is shown that Luffy, Zoro, and Nami returned to their usual outfits in the manga.

Does Robin join Luffy's crew?

Robin was the first to initially willingly join, and then officially joined after Luffy's crew came to her rescue from CP9.

How long does Robin stay with the straw hats?

While employed in the organization, she managed to stay on long-term, safely hiding away from the World Government for four years.