Allen Walker is a young Exorcist who has a cursed eye that can see the suffering of the Akuma (demons) created by The Millenium Earl. He travels to England to the Headquarters of the Exorcists where his Master has sent him to meet with the other Exorcists. The battle with the Millenium Earl and the Noah Family vs. the Exorcists intensifies when some of the best Exorcists begin to get killed by hoards of Akuma. Japan takes center stage in this end of 19th Century plot in order to not let the entire human race be turned into Akumas and the Exorcists have the power of "Innocence" that was given to them by God on their side.
The D.Gray-man anime and manga series features a diverse cast of characters created by Katsura Hoshino. The series is set on a fictional Earth at the end of a nineteenth century where the Black Order wages war against the Millennium Earl who intends to destroy humanity with his army of akuma, weapons created from the souls of the deceased when their loved ones curse God for their loss. To aid in their efforts, the Black Order scours the world for the 109 pieces of a divine substance called Innocence, which has been washed away during the Great Flood, and for people who can use anti-akuma weapons, the Innocence in its weaponized form. These people, called Exorcists, are able to effectively fight against and destroy the akuma. One Innocence, referred to as the "Great Heart" will assure their victory. However, the Earl is also looking for the Innocence and the Heart with the intent to destroy them.
The main character of the series is Allen Walker, a young Exorcist who recently joined the Black Order after training with his master General Cross Marian. When presenting himself to the organization, he is mistaken for an enemy and is attacked by another Exorcist, Yu Kanda. However, once the mistake is realized, Lenalee Lee prevents Kanda from causing further mishap. Once inside the headquarters, Allen learns he is the prophesied "Destroyer of Time" who is the only one who can defeat the Millennium Earl. As the series progresses, Allen meets many of the members of the Black Order headquarters as well as those in other branches worldwide. He eventually meets a young, aspiring bookman called Lavi and his predecessor Bookman, who follow Allen on his adventures to witness and record the events for the bookman's record. Allen also encounters the antagonist the Millennium Earl, his akuma army, and the Noah Family, a group of humans who aid the Earl in his plot to destroy humanity.