Characters:
Yes for those that are fans of clamp, its a tragic one where eventually everybody does except some of the princples. And this one's big on angst. "Its the end of the world as we know it", REM's song could have fit quite nicely in this. And its still on going, in the manga at least. The anime is no fun cause the character start killing themselves within a very short strech of time. So I'm going to give you more of a manga tinged synopsis.

There are two groups, The Dragons of Heaven and the Dragon of Earth, The DOH want to save the world as we know it, DOE want to destroy humanity and purge the earth. Kamui is the leader of the DOH, Fuuma is leader of DOE.

Kamui: princple character, our tragic hero, decides the fate of the world. Name means the Magesty of God, has the power to blow up whole building. He's tragic cause his mother dies in a fire, which is why he is sent back to Tokyo after leaving for six years, his aunt is torn to bits when one of the holy sword is released, his childhood sweetheart goes crazy and is killed by his best friend who betrays him and turns evil.

Fuuma: major villian, Kamui's friend who turns from being a pretty boring guy to a sadistic pervert who loves torturing Kamui by hurting him or those around him that he cares about.He's the one who kills his own sister, Kamui's childhood sweetheart.

Hinoto: the chief advisor to Kamui and the other Dragons of Heaven. She is a dreamgazer, a person who can see visions of the future through dreams, also can control those visions to a certain extent.

Kotori: Kamui's childhood sweetheart(she is mentioned every so often that's why I'm bothering to include her)

My favorite pair of characters:
Subaru Sumeragi & Seishiro Sakurazuka are leftovers from another Clamp series Tokyo Babylon. But the most important thing to know about them are the are two very powerful magicians, also that Seishiro has the power of illusion. Also the deal is between them is According to a bet, if Subaru could be the emotionless and coldhearted Seishiro to feel anything after a yera of living together then he would spare Subaru's life. Well nothing happened so Subabaru's twin Hokuto when in Subaru's place and was killed.

Subaru was devestated by that and also by the fact that Seishiro revealed his self as his enemy(the Sumeragi and Sakuarzukamori,both use the same type of magic but the Sakurazukaamori use it to kill)and that the person he loved didn't love him back. So he spent the next seven year plotting Seishro's demise. And again they are on opposite sides, Subaru's a Dragon of Heaven and Seishiro is a Dragon of Earth.

Well according the anime, everybody dies and humanity is saved, la de da. The Manga is still ongoing and the only character that has died is Seishiro, Subaru does succeed but he's all broken up about it and its likely he inherited his enemy's powers.
One my fav info sites is: http://oldcrows.net/rabi/x/
she has alot of info and some manga translation.