Boss

When first encountered, Boss was a smallish beetle with a glossy, caramel-toned shell, and around that time Yoko painted a Marine emblem onto his right side. Molting transformed him into a far larger creature, his body turning teal and the tuft behind his head shifting to pale green, while his horned pincers thickened, sprouted a second pair of points, and opened small vents at the front that let him exhale flame. The Marine marking survived the change, riding along on his new shell.

Courageous and sharp-minded, Boss will go to any length to shield Little East Blue, even offering to surrender himself to the Amigo Pirates so the rest of the island might be spared. A competitive streak runs through him too, and he relished squaring off against Luffy, refusing to fold and pushing for a rematch. His deepest tie is to Yoko, an orphaned girl who had lost her father to pirates and saw something of him in the beetle.

By the Amigo Pirates' account, Boss had fled the menagerie of super-animals that Shiki the Golden Lion was breeding to conquer the world, after starting out as a creation of Dr. Indigo. He made his home on Little East Blue alongside Yoko, an orphan who came across him in the forest after the death of her father, and grew attached, and from then on he kept watch over the island. Unusually for a beetle, he never stops growing, shedding his shell roughly once a month and emerging stronger each time, able to spit fire from his horn and to shrug off blows as heavy as Franky's Coup de Vent or Luffy's Gomu Gomu no Bazooka, recovering by burrowing underground overnight.

Before learning Yoko owned the beetle, Luffy hoped to recruit him as a tenth crewmate, then let the idea go but arranged to fight him once he had grown stronger. The Amigo Pirates struck while Boss was readying to evolve, aiming to seize him as a present for Shiki. Beaten down by Largo and Corto, the beetle agreed to go along to spare the island, only for Luffy to stop him. A hit from Luffy triggered his molt, and the renewed beetle tore into the pirates, ripping Luffy, Zoro, and Sanji free of their nets before faltering again because the rushed change had not fully restored his power. Cut loose by Zoro, he recovered enough to put down Corto and to pull Luffy and Brook out of the sea. His long-promised bout with Luffy finally happened and ended in a draw, neither willing to quit. Boss stayed behind to keep guarding Yoko and the islanders, with Luffy vowing they would settle their match another day.