The Special Episode rings are special episodes that represent a holiday such as Halloween, Christmas, Easter etc. The rings are however not free. They each cost 100 AP each and once buying and playing the certain episode, the ring will disappear and you will need to buy it again to play the episode.
Easter 2012, Halloween 2011, Halloween 2012, Christmas 2012 and Christmas 2011 are the only current Special Episode Rings that are not events, the other being the Japan Expo ring that was only available in France, Amour Sucre.
In each Special Episode, following certain criteria you will meet new characters, and unlock illustrations and new outfits that are unavailable in the Story Mode.