An excellent, if not flawless, combination of ecchi, romance, and supernatural elements. The premise is that one Jae Hyuk is leading a cursed life, parentless, and forced to support his terminally sick brother through multiple part-time jobs. Then one day he makes a fateful turn in the park and gets his chest partially blown off by a stray shot from Serin. Lucky for him, she's a necromancer, and she revives him and takes him with her to the world of Chaos. From there, what starts out as a typical "student in school looking for an out" sort of affair (think Rosario+ Vampire) becomes something much, much, more. Some of the story seems forced; he melts the cold Serin's heart unbelievably quickly, and there is very little actual school that goes down before everything goes south, making what little there was seem disinterested. Nonetheless, the story develops very quickly, and the way the twist ending is based on such a simple deception (I won't spoil it for you, but it involves his brother) is almost savagely exquisite. There are a few cheap moments late, like how the apparent harbinger of the god of chaos, a sweet girl whose abused history begged exponentiation, simply melts away and dies to reveal the true danger, but the overall execution is excellent, and there's a lot of blood and gore, but not so much so that it should scare anyone away. The ending is a cliffhanger, as the big bad flees the scene, and leaves any apparent way of accessing him shut tight. If you like your high-octane supernatural fighting manga with a dash of ecchi (or you can at least tolerate it) and LOTS of frilly dresses, you'll love this series.
The continuation, though, is much bleaker and very depressive.