I had a 5* Miyuki (with the miko outfit) from the preregistration event , meaning you had to register an account before the game started last week
As for your own code, various japanese people try to get their own code "advertised" in (some wiki) lost zero sites/boards or bbs'
With my current luck, i have now a 6* Erika and a 5* Mari from my 10 cards draw with 15 gems x_x
edit: made a screenshot