Like the Shichibukai, the Nanatsumi are seven extremely powerful individuals, Pirates, mercenaries or any other faction of criminal. They are a secretive, covert operation, more secretive than the CP9. The governnment decided that the Shichibukai are being defeated so eaily is their reputations; so in order to become a member of Nanatsumi, the members are erased from history, all bounties and wanted posters are retracted. Also, the Nanatsumi have almost no restraints on their actions, well, less than the Shichibukai at least. Their former status and even race is overlooked, shown in the case of Triton Sedna, a Merman.