I am currently reading this manga. It isn't the best art, but the author keeps the character detail almost insanely accurate throughout the series. Side characters are still used, with the same detail. Which is amazing because when you see these huge groups of people you'd think that only a handful will be focused on.
That and the story is so fast paced, within 30 chapters 5 significant battles have taken place. Can't even tell you how long it takes just for one bleach or naruto battle.
the prelude needs
a) A finished manga
b) A second season
It could have a second season, basing it on Ga-Rei. But the likelyhood of that is meh.(Ga-Rei zero was like 7 episodes, all in HQ format. If they did Ga-Rei it would probably take way too much effort. Especially since when i'm talking about significant battles, its like a whole arc in One-piece or naruto.)