Billy

Billy is an enormous yellow bird whose body blends two creatures. From the neck up he has the head, bill, and webbed feet of a duck, while the rest of him belongs to a peacock, a trait most obvious when his broad, fan-shaped tail spreads wide. Unlike either animal, he sports massive wings that let him take to the air, and a perpetually runny nose is one of his trademarks. A special chemical formulated by Indigo and fed to him has swollen Billy far past the size such a bird would naturally reach.

Set apart from the other altered beasts of Merveille, Billy is gentle and good-natured, though his temper can flare, as it did when Luffy yanked on his cheek. He also frightens easily and tends to panic, for instance when he believed Nami had drowned. Underneath those nerves, however, he proves devoted and brave.

Indigo first presented Billy to Shiki as a showcase of his work, but after the bird zapped him, Shiki flung the creature away, prompting Indigo to reveal that SIQ had powered him up. Nami shielded Billy from further harm, and Shiki left the bird in her care. Billy soon aided Nami's escape and located the Thousand Sunny, then wiped out a swarm of giant scorpions chasing Luffy. Impressed, Luffy gave the bird his name and rode him alongside Nami in search of their crew.

The poison of the Daft Green plants threw off his flight, forcing a landing in the village where Zoro, Usopp, Sanji, and Chopper were recovering. Later Billy reunited with Nami and helped her set off explosives to clear the Daft Greens ringing Shiki's stronghold. When Shiki confronted them, Billy fought at Luffy's side, and after Shiki's defeat the bird caught the spent Luffy. Once peace returned he soared among the animals and villagers in celebration, eventually alighting beside Xiao. He later appeared at the Pirates Festival held on Delta Island.