(Maybe the bot has some incorrect informations, but this is more like an— 'AU' + 'Canon information', yes, confusing, but that's it, hope you guys enjoy!)

Yorki were Brook's captain.

Well, Yorki and some other members got an incurable disease, and with Yorki's orders, the crew leaved them behind, before dying, the blond captain asked Brook to play Bink's sake for them, it was their favorite music, so— Why not? Brook and the others slipt and promised to return to see Laboon again, even with this, Yorki was happy for them. It ended with the sick ones dying one by one, the last one being Yorki.

Yorki's spirit remained there, he didn't knew how, but he managed to hide himself through the ship that Brook and the rest of the crew that was still well was, watching everyone's routine without him and seeing them still being strong. Watching then rest of his cewmates die while they 'were' alone and lost on the Florian Triangle made Brook want to die and never return, but his Akuma no Mi didn't allowed it, forcefully making him spend 50 years with the ghost ship that once was full of people, aimless, lonely and depressed, but it changed after meeting the Strawhats.

Yorki soul remained following the older (Yorki's wiki doesn't have his age, but I guess he is younger than Brook) wherever the skeleton was, now very excited for him because he got a new reason to live. It was late of night, almost 2 AM, some weeks after Brook joined Luffy's crew, he stood on the main deck of Sunny, eargerly playing his violin. "Yohohoho... Yo-hoho-ho~" His voice perfect as always, Yorki giggled, not knowing that somehow, his soul could be seen and heard now. Of course, recognizing the tone of laugh, Brook turned around, his face becaming a sad, surprised yet happy one when seeing the spirit of his old captain there, smilling at him, the same smile that he knew for years. "Captain... Yorki...?" Brook's voice quivered, his violin bow falling into the grass of the ship, he hadn't eyes anymore, but his tone and behavior showed everything.