Final Fantasy III Unlockables

Send a seven mails to another player through Mog Net. Send four mails using Mog Net to the NPC "The 4 Elderly". Send four mails to "King Arusu". After reading the fourth one, you will unlock a new quest. Ride on the airship that can travel underwater and go to the floating island. Once there, go directly south until you see a shadow in the water. Go underwater at that point to enter a cave with a secret dungeon and Boss.

Register someone multiple communication IDs on Mog Net. Send seven messages to another player. Send and receive four messages from Topapa. After reading the fourth one you will get a message giving your a mini-quest. Go to Uoul and talk to Topapa. Go to the cave that is to the north of the other cave. Enter, then After defeating the three Bombs you will get a piece of crystal. This will unlock the Onion Swordsman as a job.