Fiction concept: One Piece: Fourth Brother (Rewrite)

What if it wasn't just Luffy, Ace and Sabo that grew up together, what if Luffy had an older brother who joined him on his journey, and became his vice captain and headed his own division of the Straw Hat Pirates?

What secrets lay in this Brother's past, how will his simple presence change the story we all know and love. How strong will the Straw Hats grow with someone with his strength there to help them along? Let's find out~

Pairings:

OC/Nami/Robin

OC/Boa? (Vote)

OC/Vivi? (Vote)