With Niss in your party and 1 Sealed bead in the inventories, go to Iceberg and use an aircraft to fly to the top of the Iceberg and enter the steel door. Go to down and to the big room in the north-east. Talk with bead protectors there and battle with the dragons. They will tell you more about Niss.
(Rewards: Sealed bead*1, 15% EXP Capsule*1)