This is a short prequel story which is supposed to be an introduction to the series. It is also a freebie, so I will not spend too much time describing the plot or the world. Basically there are bad guys called Sky Beasts who use their powers for entirely selfish reasons and there are good guys called Sky Ghosts who try to protect the innocents from their power-hungry counterparts. This resulted in a practically all-out war invisible to outsiders.
Pain (Patricia) and Marco are two friends of the good guys' team. They used to hate each other's guts and beat the crap out of each other, but this is another story. This time they decided to spend some quality time hunting Beasts (This is Pain's favorite pastime with Marco hanging alone for the company). Lots of fights that would make Quentin Tarantino giving up filmmaker's career in shame follow.
I always find hard to review a short story as there is always an ever-present danger to writing a review bigger than its source material. This is a big no-no in my book. So let me take the following approach: I will take a look at the description and just say if the story delivered what it promised. This is an introduction to the series? In this it works perfectly fine. I would also like to note that this is the most violent story of the series so far.
So a short introduction to the series, decent one too; 4 stars.