User blog comment:Jrotc193/Caribou uses?/@comment-3060121-20120201221245

I think he was used in order to introduce a strong rookie at saboady, and someone to show the Straw Hats growth. Also, seems as of now he was really placed in order to tell the unknown person this info, after which he will probably be killed. Once the person finds out this info it will bring someone who will take over fishman island before Luffy, or challenge him once he gets it. And someone for us to laugh at.