To the people that do not understand what an AU is, its an alternate reality. This series, like the other three (Kannazuki No Miko, Kyoshiro To Towa No Sora, and Zettai Shoujo Seiiki Amnesian) are stand alone series.
You do not have to read or watch any of the previous series to understand what is going on in this one, because the mangaka always explains the core plot of each and every series.
I have read and watched the previous series, and let me tell you all one thing, the only series I recommend you guys watch is Kannazuki no Miko and I actually recommend you guys watch it dubbed as the VAs are actually pretty amazing. Himeko has the VA of popular characters such as Hinata from Naruto/Orihime from Bleach, Chikane also has a superb VA, Rukia from Bleach. I honestly prefer the dub over the sub.
Yes, the mecha battles are crap, but the rest isn't all that bad.
I am liking the premise of this one thus far. No mecha battles, yet, and Chikane is not worthless here. All the recycled characters like Souma, muscle dude, and maybe even Tsubasa (Souma's brother in KnM) seem to have gotten a genderbend, which is fucking awesome cus that means more yuri for us. The art is so much better too. Not messy at all compared to the Mangaka's previous works.
My only complain is the fast pacing. Wish he would make it longer and let us enjoy the time the girls spend together and watch how their relationship is being built, even if its fake.
Yes, the dub is very good and is the main reason I still love their english VA's(still need to get Michelle Ruff's autograph for my KnM poster so that I'll have the both). The only gripe is leaving off the "chan" from Chikane-chan. Would add that Himeko/Hinata/Orihime's VA is also the redubbed Sailor Moon and Chikane/Rukia is also Yoko Littner and Luna from Sailor Moon.
I would also recommend the original KnM manga as it has a very different flavor than the anime that it spawned, though the scanlations have varying translation quality and I don't think you can find the official release anymore (my copies are over 10 years old).
I still love this series so much even after all these years.