User blog comment:Omega natsu2/Chapter 371: Tartarus Arc, Part 2: Song Of The Heavenly Dragon, Predictions./@comment-86.70.179.7-20140210084523

there is one thing in this which made me remember something, if you search with google about the celestial keys and you add the word "dragon", you will see there is new set of keys sold in Japan with one which hasn't appeared in the manga yet, and if you look carefully, this key is open the gate of the constellation of the dragon, do you think Mashima will introduce it.

here a link : http://www.google.fr/imgres?sa=X&biw=1280&bih=903&tbm=isch&tbnid=WUJkWgdKx3X8JM%3A&imgrefurl=http%3A%2F%2Fwww.aliexpress.com%2Fstore%2Fproduct%2FCosplay-Fairy-Tail-Lcuy-Celestial-Spirit-Gate-Keys-set-21pcs-or-18pcs-and-send-Fairy-Tail%2F529359_1139437555.html&docid=XmtgYCdk5-L_jM&imgurl=http%3A%2F%2Fi01.i.aliimg.com%2Fwsphoto%2Fv1%2F1139437555_1%2FCosplay-Fairy-Tail-Lcuy-Celestial-Spirit-Gate-Keys-set-21pcs-or-18pcs-and-send-Fairy-Tail.jpg&w=307&h=305&ei=NJD4UtLPD6ay0QWzjYDoDg&zoom=1&iact=rc&dur=689&page=2&start=29&ndsp=30&ved=0CPYBEK0DMDM

look at the key next to Crux's