Sabo Introduced As Aces Pirate-Dream Partner At Gray Terminal

Ch. 583 introduces Sabo (age 10) with a full name-card (“SABO (AGE 10) (A BOY WHO LIVES AT GRAY TERMINAL)”) and gives him equal narrative weight to Ace — his five-year partner in a hidden treasure stash, both saving to buy a pirate ship (p. 12). A backstory character framed this prominently, plus the shared pirate-fund prop, are a chekhov-explicit / prop-tell that Sabo matters beyond the flashback.