What is the fastest way to get gold in Lunia

The easiest way for all people of all levels to get money is to do random box key quests and selling them for 12-17g (I recommend 12 but sell for 20 if you get a sucker). Make sure you don't level up too fast if you really want money or the easier key quests will not be available and you'll have to do 6-10H, 5-10L, or 6-10L. I doubt you would want that for just 12-17g.