Demon child Nico Robin vs. Pirate Empress Boa Hancock. I know what you are saying but OP isnt such a boring place that we know the outcome of every fight. Okay its true that Nico Robin has shown more than once that she is no match for a shichibukai this is true but I think croc said it best qoute on qoute "Hah! You never do know how two abilities are going to match up". Im unsure if Boa's merrow powers will work on robin. Both have hax powers!
Scenario 1: You judge them by their already shown feats(what they have been said to posess falls in the second scenario).
Scenario 2: Let your mind run free with all kinds of powerscaling and made up things your sure to mention anyways