Prologue.
Sacrifice
Somewhere in the back of their minds, they knew it.
That this day would come.
No one who manages to defy the World Government is allowed to live.
She had tried to sacrifice herself so the Straw Hats wouldn't have to live the life she did. But they had ignored her offer and made the choice to save her, knowing well the consequences. Even after Enies Lobby was destroyed and Robin rescued, when Luffy was offered a position as a Shichibukai, he had turned it down.
This was their fate.