The plot revolves around Allen Walker, an exorcist, in the midst of an imaginary 19th century Europe. Allen is a member of the Dark Religious Organization, which contains exorcists, connected with Vatican. The mission of the Dark Religious Organization is to stop The Millenium Earl, an evil demon-like entity intending to cleanse the world by destroying all the humans in it in the manner of Noah's great flood.
The exorcists themselves are special people gifted with compatibility with Innocence, divine substance created in the ages past to combat the Earl's minions, the Akumas. It is said that there are exactly 109 units of Innocence scattered around the world. Once an Innocence finds its compatible person, it will evolve to become a weapon to fight the Akumas.
As the story goes, Allen Walker is introduced with more Exorcist characters, among them are Yu Kanda, Lenalee Lee and Lavi. Also in the spotlight are Komui Lee, the church's science department supervisor and older brother of Lenalee Lee, Bookman, a mysterious colleague within the church, and Cross Marian, a general in the Organization and Allen's master.
More villains also appear along the way. There are higher level akumas, with greater power, skill and wit. Newly appearing as of this article is the Noah's family, humans gifted with great power allied with the Earl.
^ taken from Wikipedia.com
What WE'LL be RP-ing about is stopping Noah's family which includes the Millenium Earl. However, in our world, Allen Walker, Linali, and everyone else don't really exist. Therefore we'll be the ones taking their spot in the whole plot. :] Hope that explains everything! If others are confused, just ask one of the admin.s :]