With eyes like polished obsidian, he wears a perfectly sadistic smile. This demon in the form of a man, ever beautiful to all who see him, boasts a ferocious body able to tear his foes apart bare-handed if he must. This priest and onmyouji from the Heian period was also known as Douma Houshi or Zou Douman. He was a monster who stood opposite Abe-no-Seimei, the greatest Heian sorcerer.

He is classified as an Anti-Hero not because he is a hero who protects people, but because he seeks to harm people with vicious relish, and his death brings peace to the world. He was known to have inflicted damage upon Fujiwara-no-Michinaga, a prominent leader of the times, through a curse. Unlike Abe-no-Seimei, who belonged to the Onmyou Bureau, Ashiya Douman was a priest, and considered to be part of the opposition to the government.

Ashiya Douman the Alter Ego is quite different in nature than the Ashiya Douman the Onmyouji priest of the past. In order to establish himself as an Alter Ego, he fused a combination of three Divine Spirits and vengeful spirits, into his Spirit Origin to become a High Servant.

The Divine and evil spirits fused into Ashiya Douman were as follows:
The first one, Itzpapalotl, a goddess from Aztec mythology.
The second one, Chernobog, an evil god from Slavic mythology.
And third, a vengeful spirit from Japan's Heian period, known as the "Akuryo Safu."

Ashiya Douman in this game is the clear antagonist of the capital and the people Abe-no-Seimei protects. He is deeply in touch with the five elements, at times acting as a transcendent being who manipulates even nature (the gods), and viciously mocks all things that are small and fleeting, as well as civilians who live humble lives. He also takes pleasure in trampling on human pride and faith (which explains Musashi's intense loathing of the Alter Ego).

As he manifested as an Alter Ego class, he is not the persona of the Ashiya Douman who actually existed in the past, but is rather a caricature of the historical figure. However, Murasaki Shikibu's accounts imply that the historical Douman was quite monstrous as well.

The Ashiya Douman who was summoned to Chaldea has no recollection of serving the Foreign God in opposition to Chaldea...or so his behavior seems to suggest. He claims to have no idea why how or why they were summoned as an Alter Ego who possesses far greater power than could have been possible during his lifetime.

This is an obvious lie.

Douman was, without question, the very same Alter Ego who fought Chaldea somehow summoned to Chaldea while retaining the memories of the Douman who desired to become the dark sun. Could this have resulted accidentally from a connection with Chaldea, or could it be Proper Human History simply ignoring the background and motivations of a person, so long as they are powerful, or could this simply have been something Douman planned for? (Though, it's never been proven whether a Heroic Spirit's desires can directly influence their summoning or manifestation.)