You have to find all of the Orichalcum+. You get one by getting every single moogle mineral, shard, stone, etc. You also find the recipe for it in the hallway that leads to the pod room where Sora was asleep for so long.
After defeating doga and unei (sorry if it is a spoiler)
go straight to the tower in the middle of the crystal tower click on the door and you will be in forbidden land eureka
you can get
The...
send 7 or more wifi mails, send 4 mails to princess sara, and she will say her pendant broke. talk to takka, send 5 mails to takka, send 4 mails to cid and kill aeon. aeon will drop a metal, cid says...
This depends on whether you have KH or KH2. If you have KH2, you must get all the crystals, an Orachilum, and all 13 Orachilum+, and the Ultima Recipie. Then go to a Moogle and Synthisize. In KH1,...