This is a technique seed, not a single-reveal seed. The pattern recurs at every later arc with at least one of the following inversions:
Chopper’s flag at Drum Island — Hiriluk’s pirate flag is the thing left behind; Chopper raises it and defends it. Same structural beat as Chouchou guarding the shop; the dead master’s love-object is the locus of the vigil. (~Ch. 152-153)
Brook’s Laboon promise — Rumbar Pirates dead; Brook (and Laboon, on the other side of Reverse Mountain) keep faith with the dead crew’s promise to reunite. Same beat: the dead are gone; the animal-companion (Laboon) and the lone survivor (Brook) maintain a vigil at the agreed-upon meeting point. (Ch. 442-489; opening flashback Ch. 103 Laboon).
Pell’s vigil over Vivi’s mother’s tomb / King Cobra’s body — Alabasta arc.
Sengoku-Garp-Roger triangle around Ace’s ancestry — institutional version of the same beat: the dead Roger leaves behind a son, and Garp/Whitebeard/Sengoku each guard the son in different ways.
Gaimon’s 20-year vigil on the empty chests (Ch. 22 — pp. 11-30): a variant of the Chouchou template where the loyalty is to a task assigned by an absent group (the pirate crew that sailed without him) rather than to a beloved dead master. Same structural beat: the absent party is gone; the lone survivor cannot leave the place because of the task; the vigil continues until an outside intrusion (Luffy) forces a reckoning. The reckoning here is the chests were empty all along — the loyalty was to an empty container, just as the loyalty-to-dead-master grammar in later arcs (Brook/Laboon especially) involves keeping a promise to people who can no longer collect on it. Variant captures: the loyalty-target need not be loved (Gaimon is resentful of his crew, p. 22), only unresolvable (the task was never completable). Pattern broadens from loyalty-to-the-loved-dead → loyalty-to-the-irreversible-loss.
Earliest known caller
Recurring beat. The structural template is recognizable on first read to anyone familiar with Japanese folktale tropes (the Hachikō story of the Akita dog who waited at Shibuya station every day for 10 years after his master died is the direct cultural reference — Oda is openly importing it). The Hachikō reference makes the technique immediately readable to a Japanese audience; non-Japanese readers can call the technique on its second instance (Chopper / Hiriluk).
Why this matters
Establishes Oda’s animal-companion-as-emotional-mirror technique as a recurring grammar element. Every later major Straw Hat backstory has a version of this beat — a loyal-survivor-at-the-place-the-loved-one-left-behind. The technique stack:
Prop-tell — the dead person’s thing (shop, flag, station, ship) carries the loyalty.
Animal-companion-mirror — the animal can’t process the loss verbally, so they process it spatially (by staying).
Slow-drip — the backstory is delivered by a third party (Boodle here; later Dr. Hiriluk’s flashback, etc.) while the animal remains silent on-page.
Character-as-foreshadowing — the animal is not just an animal — they’re a structural stand-in for the soon-to-be-revealed wound of a major character.
Luffy — the silent recipient of the parable (page 15 — changes his behavior in response)
Nami Hates Pirates Tell — companion seed; Nami is in the same chapter sequence as the listener for the parable. Both are backstory-via-empty-place seeds planted within ~3 chapters.
Hat Handoff Promise — Luffy’s own version: the straw hat is Shanks’s left-behind thing, and Luffy is the vigil-keeper.