Warning*** This story contains themes of religion and incest that some readers may find offensive***
Setsuna is not what you would call ordinary. First of all, his best friend is a sword, Seven Blades. Secondly, there's the fact that he's the reincarnation of one of Heaven's most powerful angels, Alexiel (a female angel!). And then there's that little detail about being in love with his sister, Sara, who happens to be in love with him as well. The series focuses on him searching Heaven and Hell for her and ultimately he gets drawn into the war between Heaven and Hell.
Characters: (there is a huge cast of characters in this manga, that are all focused on to various degrees...these are just my favorites)
Setsuna: At first, Setsuna has no interest in the destiny that is his just because he's the reincarnation of Alexiel, worried more about Sara than anything While those he meet keep trying to draw him into the fight, at first he refuses to be swayed from his goals. Eventually he matures and this combined with his loyalty towards his friends makes him a great hero.
Rosiel: The crazy, younger twin of Alexiel, he's destructive and doesn't really care who he hurts much of the time. He's also determined to bring Alexiel back. As more of his story is revealed though its hard to know if you should hate him or pity him.
Michael: My absolute favorite character even before I read the manga (I loved how rebellious he looked, and that tattoo was awesome). He lived up to all of my expectations and more. He's hotheaded, rebellious and has a brother complex (as well as a height complex...lol)
This is a complex story that, at times might be confusing, its also rather slow to start, taking the first three volumes to build up the basis for the whole rest of the story. If you stick with it thought, you'll find a story with lots of depth, with a cast of characters you really get to know and care about, learning about their past as well as their present. You don't always know what side a character is on, or what side they'll end up, and I in know way was able to predict the ending, which tied up everything nicely.