The story is set in an industrial Western world with several countries in Europe and Asia featured, to the extent that you could draw a parallel between D Gray Man and Fullmetal Alchemist. Allen Walker, the key character, is intent on becoming an "Exorcist" under an organization called the Black Order that combats the antagonist, the Millennium Earl, who's rotundity and nonchalance that I think at times does not appropriately suit the sinister image of the villain. A good portion of the story revolves around the Black Order's missions to obtain the divine substance know as "Innocence," which grants users power to combat the Akuma ("devils"), minions of the Millennium.
In the Black Order, Allen meets the easy-going Lenalee, the hilarious commander Komui, the carefree Lavi, and the uptight Kanda. In describing the characters, however, one-word adjectives simply does not suffice. A strong point of this anime is the character development of Allen and several of the supporting cast, including the many characters that are introduced throughout the series.
You will find a bit of unconventional biblical elements and old medieval folklore, an instance of which is one of the initial villains - the vampire Arystar, whose story is a bit unique and becomes a supporting character later in the series. The story of Noah and the Arc is prominently featured, modified into the background of the antagonistic Noahs, elite servants of the Earl.
Regarding the music of D.Gray-man, the opening and ending themes were quite memorable and catchy. Although many people were indifferent to the soundtrack, I personally thought it contributed greatly to the melancholy tone of the story that frequents the plot. The stand-alone piano tracks were very beautiful, especially the "14th's Song" that was featured much later at a pivotal point in the series.
As a final word, I reiterate that D.Gray-man may seem like your typical shounen anime, but provides quite a refreshing, supernatural story and setting.
