Among One Piece's Straw Hat Pirates, Brook is one of the most overlooked by fans. This goofy pun-loving skeleton is still the one afforded the least amount of screentime, and, to be fair, his "perverted" antics do get tiresome. However, to say this 90-year-old skeleton musician has no depth and can only play one tune would be a great misunderstanding of the character. Brook isn't without his flaws, but this skeleton has heart, and his backstory is one of the most heartbreakingly sad among the Straw Hat Pirates.
The Straw Hat crew is first introduced to this goofy skeleton at the start of the Thriller Bark Arc, and he makes quite the first impression. The skeleton says he died 50 years ago, but thanks to eating the Revive-Revive Fruit, he was given a second chance at life. The manga proceeds to reveal his backstory in a non-linear fashion, gradually revealing the full picture of who this jovial pun-loving skeleton really is.
50 years before Luffy first set out on his journey, Brook was a crew member and musician of a merry band of pirates called the Rumbar Pirates, hailing from the West Blue. While out at sea, the crew stumbled upon a lost baby whale, so to lift the child's spirits, they played one of their most jovial shanties, "Bink's Sake." After that, the baby whale started to follow the Rumbar Pirates on all their adventures, and they gave him the name Laboon.
Brook and Laboon became very close, but eventually, a difficult conversation needed to be had. The Rumbar Pirates' next voyage was to the Grand Line, and a sea as chaotic and dangerous as that is no place to bring a baby whale. After two months at the Twin Capes with Laboon, they left the young whale behind with the lighthouse keeper Crocus, promising Laboon that they will come back in a few years when they finish sailing around the world. Laboon takes this promise to heart and so the Rumbar Pirates say their goodbyes to the youngest member of their crew with the promise they will return through Reverse Mountain.
Three years later, the whole Rumbar Pirate crew was dead except for Brook, all alone as their ship floated through the Florian Triangle. Chapters 487-488 of the manga do well making readers sympathize with Brook, as the chapters intercut The Rumbar Pirates' voyage and skeletal Brook alone in the Florian Seas. The once jovial lively sea vessel is now a painfully empty and quiet ghost ship, with only one skeletal passenger left trying to preserve his sanity.
It's easy to write off Brook as an annoying character, and his humor is certainly not for everyone, but his backstory clearly shows how he became this way. How does one manage to stay sane alone on a ship for 50 years? Brook did it by trying to make himself laugh. It's heartbreaking watching Brook doze off and then see his crew alive and well, only for reality to set back in as he wakes up from his dreams. Brook needed a way to cope with his loneliness and that manifested in a sense of humor that hasn't adjusted to being around other people in five decades.
So what exactly befell the rest of the Rumbar Pirates? Half the crew, including Captain Yorki, contracted an incurable illness and left the ship so that the remaining men would not fall victim as well. With Brook becoming the acting captain, things were smooth sailing until an enemy pirate attack in the Florian Triangle. After the firefight, the remaining crew met their slow deaths from poisoned weapons, regretfully unable to keep their promise to Laboon.
However, knowing that Brook's devil fruit could still revive him, the crew spent their last moments recording the whale's favorite song, "Bink's Sake," so Brook can still take it to Laboon someday. The scene of the pirates singing to their final breath is equally heartfelt and heartbreaking. The anime adaption of this scene is even more distressful than the manga version, showing the quintet of musicians collapse one after another in tempo, leaving behind just Brook to carry the accompaniment.
Brook wasn't even sure Laboon was still waiting for him until Luffy told him, but he still planned on coming back to the Twin Capes regardless. When Luffy told him, all the dry skeleton could do was cry his heart out and be grateful that he's alive to keep his promise.
Brook is a man who values a promise above all. He cherishes the promise he made to Laboon to return to after sailing entirely around the world, he honors the promise he made to his former crew to give the final song they played together to that very whale and he upholds his promise to Luffy to be his loyal musician and help him reach his goal of becoming King of the Pirates. Brook's trustworthiness and reverence for his friends are what makes him worthy of being a Straw Hat Pirate, and far more complex than his jokey demeanor might imply.
