Why Is Nico Robin Working With Cp9. Rob Lucci Kaku Bleuno and Kalifa may have a chance if they work together and take advantage of the Door Door Fruit. Since she reached the age of eight and her homeland was destroyed she survived by joining shady organisations gaining experience in skills like assassination and then destroying them from the inside out.
Could it have been a test. Nico Robin Crocodile eventually betrays Robin and leaves her for dead but Luffy ends up saving her life which is why she appears on the Straw Hats ship at the end of the arc and asks to join them. But as you said it wasnt necessary in most situations but it would make things easier.
Nico Robin is the archaeologist of the Straw Hat Pirates.
Ok background on my theoretical madness here. Losing her will to live. Nico Robin leaves the crew. Could this have all been a plan by Aokiji.