(Pending — the Caesar rematch / how Luffy beats the oxygen-denial is forward of this window.)
Earliest known caller
(TBD.)
Why this matters
A chekhov-explicit combat-problem install: Oda recaps the exact mechanic (oxygen removal) that already beat the protagonist, framing the win-condition for the rematch before it happens. Cross-link Caesar Clown, Luffy, Gasu Gasu no Mi.