(Partial in-arc — Oars is reanimated and wields power forward of this window (~Ch. 458); the long-range significance of the ancient-demon legend/lineage is forward. Left pending.)
Earliest known caller
(Unrecorded.)
Why this matters
Oda background-symbol + chekhov-explicit: an enormous, named threat is installed at the end of a chapter as a chained, frozen corpse, with its entire mythic pedigree pre-loaded (“Continent Puller,” “created a nation of villains,” “land of ice”) so the eventual revival lands with weight. The ancient-demon framing also plants a lineage seed that resonates far beyond Thriller Bark.