Byojack is an old man with a white beard and a green coat on. He wears a horned helmet that has one horn missing like World. He is as short and skinny as he was as a child, due to his disease.
He often opposes his captain's plans, suggesting that they are illogical. He seems to care for his crew and wishes for his captain to view them all as companions again, despite World viewing them all as traitors.
Abilities and Powers
He is weak and fragile from sickness, and usually sits on World's shoulder. His fighting strength is practically nonexistent. However, as the World Pirates' vice-captain, he likely has command over the crew, save for the captain.
Despite his lack of combat skills, he still plays an important role - gathering information for the World Pirates. He does so by using several Den Den Mushi with which he can eavesdrop on Marine and World Government conversations, making him very well informed. He also seems to act as a sort of adviser to his brother, making him seem quite wise when making choices.
During his birth, or at least sometime as a child, Byojack acquired an unknown disease that prevents him from getting taller than he is now, and makes him incredibly weak. The disease wasn't life-threatening, as he lived to over 80 years old. Byojack told his brother World of the sea, and how the world is filled with many adventures, and he should go to sea. World agreed, but insisted on bringing his brother, too, and eventually, Byojack agreed.
When they grew up, they soon formed the World Pirates, having gathered various crewmembers. After clashing with several pirates and Marines, they were viewed as a major threat to the Government. When the Marines laid siege upon the crew 30 years ago, Byojack and the other crewmen retreated, leaving World to be captured and locked in Impel Down.
After his brother escaped from Impel Down, Byojack reunited with his brother but became increasingly worried as his brother focused more on revenge than his crew. He was present when World captured Hancock's younger sisters and informed his brother and the crew about the condition of the battles that happened on their ship.
Byojack reminded him that they fought for him and recounts their original dream together. Byrnndi once more ignored Byojack's pleas and went down to the room where Mari and Sonia were being held. Luffy arrived there and once more confronted Byrnndi in battle. When the Marines arrived Byojack reported this to Byrnndi who saw it as an opportunity to get his revenge on the Marines. When Byojack objected, Byrnndi revealed that he was just using him and the ship to carry out his objectives and saw no more use for him. Luffy, overhearing this, saved Byojack from Byrnndi's attack, angered that Byrnndi would treat his brother and friends so callously. After managing to form Haki over both his arms, Luffy was able to knock Byrnndi down.
Luffy and Byrnndi engaged in one final battle with the latter once more mocking him for being unable to save Ace. Byrnndi recovered and decided to use the cannon despite Byojack telling him he's too weakened from his fight with Luffy. Byrnndi knew this however and apologized for his treatment of his crew before heading off. Using his powers, he launched a gigantic cannon at the Marines. But just as it was about to hit, it got sliced in half by Mihawk. Having used the rest of his strength on that attack, Byrnndi fell over. Byojack, still loyal to his brother after everything, stayed by his side as the Marines inevitably blew up their ship. He was presumed to have died in the explosion alongside his brother.
- Being Byrnndi World's brother, it can be assumed that his full name may be Byrnndi Byojack. However, there is no official mention of it, being simply referred to as Byojack.
- The symbol in his serum bag resembles Donquixote Pirates' Jolly Roger, but being inverted and not crossed out.