Set in an alternate 19th century, it tells the story of a young Allen Walker, who joins an organization of exorcists named the Black Order.

They use an ancient substance, Innocence, to combat a man known as the Millennium Earl and his demonic army of Akuma who intend to destroy humanity.

The story follows a young exorcist named Allen Walker who has been spending several years of training under his mentor Cross Marian to defeat machine-like creatures known as Akuma created by a man known as the Millennium Earl.

Once finishing his training, Allen travels to the Black Order which is primarily composed of other exorcist and several supporting staff members.

Allen learns from his new superior Komui Lee that the Anti-Akuma weapons are actually powered up by a divine instrument known as Innocence and that the exorcists' mission is to recovering it alongside a "Heart" before the Earl.

Besides being confronted by Akumas that are evolving into stronger foes, Allen is shocked to find that there are humans with supernatural powers serving the Earl, Noah's descendants.

Arriving in China, the search party learns that Cross recently left for Edo, but his ship has been lost at sea.

In their journey to Edo, Allen splits from the group to face the former exorcist Suman Dark who is being tortured by the Innocence as a result of betrayal.

This eventually leads him to his obsession with hunting the Akuma again as he can see their tormented souls through the eye that his adoptive father, Mana, placed on him years ago.

[7] During production of the first anime adaptation, the author often visited the TMS Entertainment studio, where the voice actors requested advice about their characters.

Although Hoshino was nervous about talking with them, she was surprised by their dedication in practising their characters—particularly Sanae Kobayashi (Allen), Takahiro Sakurai (Kanda), Katsuyuki Konishi (Komui), and Hiroki Tōchi (Cross Marian)—and joked that Lenalee seemed more beautiful after she saw Shizuka Itō's work.

[28] In August 2017, Funimation announced they would release the series' second half on home media version starting on October of the same year.

[34] According to Funimation Entertainment president and CEO Gen Fukunaga, the anime series was popular in Japan and the United States.

[39] Noting that Allen's use of the anti-Akuma weapon might seem clichéd, Todd Douglass Jr. of DVD Talk found its use in the anime entertaining.

[44] Tonhat also praised the Earl's modus operandi of reviving the dead as Akuma, seeing it as a strong theme that allows viewers to sympathize with his victims.

[43] Neo found Junpei Takiguchi's work as the Earl Japanese actor highly superior to the one from the English dub, Jason Liebrecht.