Brook officially joins the Straw Hat Pirates at the end of the Thriller Bark arc, in manga chapter 489 and anime episode 381, titled “A New Crewmate! The Musician, Humming Brook.”

When does Brook join the crew?

  • Brook first meets the Straw Hats on the ghost ship in the Florian Triangle, where Luffy immediately invites him to join, but Brook declines because he has no shadow and would die in sunlight.
  • After the events on Thriller Bark and the defeat of Moria, Brook resolves his shadow issue and is finally free to sail again.
  • His official joining happens when he asks Luffy once more if he can join, and Luffy happily accepts. This is:
    • Manga: Chapter 489 (“The Eighth”)
* Anime: Episode 381 (“A New Crewmate! The Musician, Humming Brook”)

Mini timeline

  • First encounter with the crew: Florian Triangle / ghost ship, pre–Thriller Bark proper.
  • Initial invitation and refusal (because of his missing shadow): early Thriller Bark.
  • Shadow problem resolved and decision to sail again: later in Thriller Bark.
  • Officially becomes the Straw Hats’ musician and ninth member: Thriller Bark finale, episode 381 / chapter 489.

Why Brook decides to join

  • He wants to live an adventurous pirate life again after decades alone, and the Straw Hats match that dream perfectly.
  • A huge part of his motivation is fulfilling his promise to Laboon by returning to Reverse Mountain with strong, reliable crewmates.
  • His music and swordsmanship let him protect his friends, which is exactly what he failed to do for his old Rumbar crew, so joining Luffy feels like a second chance.

Extra: quick Q&A

Q: In what arc does Brook join?
A: He formally joins during the Thriller Bark arc.

Q: What number crewmate is he?
A: He is the ninth person to join Luffy’s crew and serves as their musician.

TL;DR: Brook truly, officially joins Luffy’s crew at the end of Thriller Bark in chapter 489 / episode 381, after resolving his shadow problem and reaffirming his dream to sail on and someday reunite with Laboon.

Information gathered from public forums or data available on the internet and portrayed here.