So they put out the codes for the closed beta players to get a special outfit.
Unfortunately, the code is only for one character, so if you have a nice costume given to you by your school you may want to give the code to a character whose school gives them an outfit that you don't like (like me and the Harmony/Zephyr school costumes.) Unfortunately for me, I used mine on my Sun Moon character and the special costume I received was a white version that doesn't look anywhere near as nice as my Sun Moon outfit (which as you can see from a screenshot earlier in this thread, looks a bit like a cross between Assassin's Creed and Prince of Persia).
So yeah.
Also, be very careful as it will only give you the code once upon logging into Arc. If you close the little pop up window you will permanently lose it. Mine was blank at first but it had 2 pages and I switched back and forth and it showed up.
Unless you got a code and don't plan to play the game, in which case, I'll be happy to take your code. :3