Ch. 131 (pp. 9-10, 15) establishes that Nami has fallen ill and lies sick below deck on the
Going Merry. The crew shields her from Wapol’s attack and the illness is treated as urgent.
This is the explicit Chekhov’s-gun that drives the entire Drum Island arc: the Straw Hats
need a doctor for Nami, which sends them onto the winter island. Structurally pre-loads the
recruitment of a ship’s doctor — the Straw Hat
Recruitment Pattern again uses an arc-quest to surface the next crewmate.