User blog comment:Whiskey13/10th SH/@comment-910220-20110102213614

Well, since seven out of nine members are male, the tenth should be a female.
 * She will join at the end of the Fishman Island Arc.
 * Most likely a mermaid.
 * Help guide the crew through the seas (Nami is the navigator, but not enough to guide through the harsh seas).
 * Mermaid, not a fruit user.
 * Powerful swimming abilities.
 * Beautiful, young, someone Sanji would swoon over.
 * Enthusiastic, excited, not violent, nice.