Find "The Sealed Letter" storybook from Dual Ghost Pirates.
Now travel to Ludi and talk the npc #1
Npc #1 will refer you to Orbis and talk to Npc #2 ( this npc should be near the guild making place )
After your done, travel back to Npc#1
The npc#1 then asks you to hunt for 3 items: Griffey Wind (Griffey), Thanatos Black Tornado (Thanatos), Boogie's Cursed Whirlwind (Zakum).
Once you collect all the required items, travel to Leafre
Talk to your 4th job instructor to finish.
NPC #1: At Ludi, go to Terrace Hall (Toy Factory) and move all the way to your left until you reach Cloud Terrace 5. There is a hidden porter slightly to your left, enter it and you will find this NPC named Unknown Thief. Talk to him and he will ask you to get the Maple Marble from NPC #2.
NPC #2: Now go to Orbis where the Guild Headquarter is. Just outside the main building, there are 3 steps, teleport all the way to the top. You will see a Maple Leaf (yes, that's the NPC #2!). Click on it to get the Maple Marble and return to NPC #1 to complete the quest. Reward: 800,000 EXP