Not so much a "special", as it is literally just the opening to "Tenchuu Girls", the anime Enju was known to love over the course of the series.
It's pretty much just your standard moe anime opening drawn in a pleasing style similar to the rest of the Black Bullet series, with a peppy and catchy opening song. I was reminded of the Purupururin opening that was made to go along with the Welcome to the NHK series, as both are just fun side things to go along with the anime viewing experience.
Don't expect this to add any real substance to the Black Bullet anime, but
if you happen to be watching, it won't hurt to check this out.