Brook

Brook died at sea with his crew and came back alone, because he had eaten a fruit that returns the eater's soul to its body once. The soul spent a year finding its way home through fog, by which point the body was bones. He then drifted for decades on a ship full of dead friends, singing to himself, waiting for a promise to become possible again.

On deck he is the gag character: skull puns, a request to see underwear delivered to anybody regardless of context, and an afro that survived decomposition because the roots are strong. In a fight he is a swordsman who draws from a cane, moves faster than the eye follows, and never needs to breathe. Brook is what happens when the joke and the threat are the same person.

The promise is a song. His old captain agreed to meet a whale at a particular island, and Brook's entire arc is about keeping an appointment made fifty years early. When the crew hears that song properly for the first time, the series does the thing it does best: sets a joke up across hundreds of chapters and then hands you the bill.