in 2018 Lucifer and his army of demons rose from the depths of hell to destroy all of humanity. Through the years 2018 to 2035 two thirds of the population were killed. Humanity was forced to throw up walls around major cities and hope for the best, until two scientist named Dr. Aleander Noctis and Dr. Kira Grace created a sub-species of Human known as the Noctis Deamona.
The Noctis Deamona are being created by combing specific aspects of human DNA with demon DNA to create a human demon hybrid. The creation of The Noctis changed the course of history and allowed humans to turn the tide in the war. Humans using Noctis were able to push the demons back into hell, still since the gates of hell remain open there will always be some demons on the surface of Earth.
Knowing this Dr. Kira Grace created an organization she called The Black Roses to fight off the demons until someone could work out how to close the gates. She also founded the five academies' schools designed to train Black Roses aka Demon Hunters which are stationed on five of the seven continents.
Over a hundred years has pasted since this time and still humanity is no closer to closing the gates but maybe there is still hope yet.