The given name サンジ (Sanji) decomposes as san 三 (three) + ji 児/路 (child/son) — literally “third son” in the Japanese kazoejun (counting-suffix) convention for boys: ichi-ji (1st son), ni-ji (2nd son), san-ji (3rd son), yon-ji (4th son). The surface reading is “three o’clock”; the encoded reading is birth-order serial number.
For 800+ chapters, Sanji was presented as an orphan rescued by Zeff with no family backstory; the name read as a quirky-single-meaning third-son name from a family the reader never sees. The encoded family was hiding in plain sight as the surname Zeff never asked about.
The payoff
Earliest known caller
Japanese readers who paid attention to kazoejun counting could (and did) parse san-ji as ‘third son’ from Ch. 43 release in 1998 — but without a second-son or fourth-son in the text, the reading had nothing to triangulate against. The family-system reading was unconfirmable until the Vinsmoke reveal at Ch. 812-832 (~2016). The fan call therefore went from fringe-curiosity (1998-2015) to retroactive-confirmation (2016) in one arc.
Why this matters
This is Oda’s 18-year-burn name encoding — possibly the longest-burn name-encoding in the series at the time of its payoff. The technique:
Pick a numeric-serial-position name (san-ji = 3rd son) for a character introduced as an orphan with no family.
Withhold the family reveal for seven hundred and fifty chapters.
Reveal the family by giving all siblings the same naming pattern, retroactively making the protagonist’s name the family-system marker that was always visible.
Generalization: when a One Piece character has a numeric-Japanese-name (san-ji, ni-ji, ichi-ji, etc.) AND an unexplained-orphan backstory, test for a withheld serial-family reveal in a much later arc. Doflamingo’s Donquixote family, Charlotte’s birth-order-by-time-of-day, and the Vinsmoke 0-1-2-3-4 pattern are sibling cases. Sanji is the prototype for numeric-name-encodes-withheld-family.