An explicitly stated, load-bearing alliance between two distant peoples — Zou’s minks and Wano’s Kozuki clan — seeds the geopolitics of the coming Wano storyline and a shared ancient history measured in a thousand years. The minks let Jack raze the Mokomo Dukedom rather than surrender the hidden Kozuki retainer Raizo.
The Road-Poneglyph / Void-Century / deeper Wano specifics are forward — seed only.
The payoff
(Pending — the bond’s deeper significance to the Wano alliance and the shared ancient history pays off forward of this window.)
Earliest known caller
(The seed is an explicit on-page declaration Ch. 816; no advance fan-call required.)
Why this matters
A textbook chekhov-explicit seed: rather than a subtle visual hint, Oda has the two kings state outright a thousand-year pact between two peoples the reader has only just met — front-loading the emotional and political stakes of the Wano arc to come. When a One Piece character explicitly invokes a “millennium” of shared history, that history is being promised as a future payoff.