Kurokami OP Single - sympathizer by Minami Kuribayashi

The Kurokami OP Single has just been released! I don't understand the release dates of these OP/ED singles. Sometimes we have to wait until the whole anime series is over to have the single, and sometimes after just 1 or 2 episodes, the OP and ED gets released!!! I wonder which ones sell better? The Kurokami OP theme song is entitled sympathizer by Minami Kuribayashi (of Mai-Hime/Otome fame).You