In the book "Representing Multiculturalism in Comics and Graphic Novels" Carolene Ayaka states another theme set in the series is identity. This is reflected in Allen and the exorcists familiarizing themselves with their own supernatural powers in order to become more humanize themselves. On the other hand, Allen's revelation that he is the 14th Noah which makes him less human. Another theme is grief, as seen in the Millennium Earl's appearance as a tired, middle-aged man who is constantly searching for a former comrade, Nea. Hoshino believes that the Millennium Earl, the series' main antagonist, would fit the manga's demographic. In the book "Anime and Philosophy: Wide Eyed Wonder" Josef Steiff and Tristan D. Tamplin discuss how "D.Gray-man", alongside "Spriggan" and "Ulysses 31", focus on the "end of the world" with "D.Gray-man" and "Spriggan" taking references from the blibical flood.