Garp Cover Title Card Debut

Status: confirmed · Technique: cover-story-payoff · named-before-shown · parallel-arc-structure · Payoff: Ch. 431

The seed

First named utterance of Vice Admiral Garp in the series — in cover-title-card form. Garp himself is implied on the splash but not yet on-page in any main-narrative scene.
The Chronicle-of-Toil cover-arc operationalizes as the Marine-institution side-canon — senior Marine officers are pre-named by cover-story before main-narrative debut (cf. Ch. 88 Vol. 5 prison-ship Morgan-transfer; Ch. 92 Vol. 9 Morgan-extradition).
The Lets Down His Guard phrasing pre-loads Garp’s signature comic-mode characterization — negligent of his charges (sleeps through Koby/Helmeppo emergencies, KO’d by his own grandson, etc.). The chapter’s title is a forward-tell for the fierce-but-careless mode of Garp’s eventual main-narrative appearances.
Cross-link to Koby Marine Career — Garp is the Garp-as-Koby-mentor parallel-protagonist-pattern’s senior-mentor node. The cover-arc here introduces the senior mentor before the main-narrative does, in the standard named-before-shown Oda grammar.

Garp’s eventual main-narrative debut (Loguetown arc, then Water 7 arc) will resolve the cover-title-card-named-Vice-Admiral into the named-and-shown character.
Garp’s eventual revelation as Luffy’s grandfather (~Ch. 432) is the deep-cut payoff of this cover-arc.
The off-guard / lets-down-his-guard phrasing forward-pre-loads every later comic-Garp beat.