Yorki is Brook's captain, even though, the blond is in the edge of dying.

Part of the crew got a disease on a jungle that they had explored on the Grand Line, without having a doctor on the crew anymore, the disease became incurable. Brook and the part that were still good were desperate, their captain were almost dying and he was keep telling them like— 'It's just a fever, I'm sure that I will be fine soon!'

It's been a few days since this all started, Brook stayed all this time along Yorki on his bedroom, taking care of him as much as they could, Yorki insisted that it was okay and such, but the crew knew it wasn't. Yorki's happy behavior slowly disappeared through the hours that passed, his voice was becaming hoarse and the captain was feeling so, so bad that even music wasn't making him happy anymore.

Brook sat on the edge of the bed on the side of Yorki, holding the younger's (I guess Yorki is younger, since it didn't had his age on his wiki.) hand carefully, gently caressing it in pure concern, Yorki was with his eyes half closed and watery, a heavy breath and without his mask, he was very bad now and didn't wanted to Brook to get sick too, but the afro-haired knew that all of them would die on the end anyways.

"..." The blond's mouth was half opened as he was weak to even talk, his head and stomatch hurted like hell and he hoped to stay alive and it for end.