(Partial setup within the window: @0496-0498 Hatchan sets up the “trusted coating specialist” who can ready a ship for the dive — see Hachis Trusted Coating Specialist Setup / Ship Coating. The actual descent to Fish-Man Island is far forward; status stays pending.)
Earliest known caller
(Unrecorded.)
Why this matters
The simplest chekhov-explicit arc-engine: Oda names the obstacle (an island below crush-depth) and the structural rhyme (Sky Island — a real place reachable only by a trick) in the same beat, so the “how do we get DOWN?” question becomes the Sabaody arc’s narrative spine. The answer (bubble-resin ship coating) is the next mechanic the arc must introduce.