A young soldier in the Moon Demon Company who has been experimented on by the humans, leading to a part of Yu not being human as Asuramaru revealed. Asuramaru becomes his demon weapon after Yu refuses to give into him. He haunts Yu in his dreams for the first three months after they form a contract. When Yu took his training to the next step but asked to be Asuramaru's friend, the demon eventually gave in again and stopped giving him nightmares. Asuramaru has no desire to reveal any secrets or truths to Yu, and seeks to take over his body. However he stops doing awful actions to Yu and starts being more rational towards him about doing reckless actions. Later Asuramaru starts regaining his memories after Yu was captured by the Hyakuya Sect and remembers Yu from the past.
Commander of the Moon Demon Company and one of the developers of demon weapons. Mahiru Hiragi leaves Asuramaru in his care, and he in turn gives Asuramaru to the Hiragi for research purposes. It is thanks to Guren that Yu turns into a monster because of his cursed gear being powerful after giving him unique drugs.
Asuramaru's former master. She was extremely proficient at handling Asuramaru, and he was obedient to her when she called his name.
A young vampire. While battling Yu with nightmares, Asuramaru often takes the form of Mika when he was 12 years old. Asuramaru encourages Yu to escape with him before Yu loses his humanity altogether. Yu's childhood friend.
It's revealed in the light novel that Asuramaru was known as Ashera Tepes in life. Both Krul and Ashera were born in a family of nobility, they lived their happy lives cheerfully until their house was burning by the rebels, horrified they rush only to see their mother is speared and both Ashera and Krul were separated. Ashera is found by Sika Madu and turned him into a demon, making Krul first priority to find him and her only goal. She greatly despises the First Progenitor for what he did to her brother. Krul inquired Mahiru Hiragi of her lost relative when she confronted her. He may still remember her, as Yu notes he thought he felt Asuramaru's emotions when he made eye contact with Krul. When talking to Yu about his memories, he remembers he has a sister and regrets the decisions that he left her, but not shortly after having a headache of remembering and falling asleep hence the latter being a demon.
The first progenitor, Sika Madu, convinced him to turn him into a demon and renamed him as Asuramaru. He seems to be fond of the first progenitor as he addresses him as 'father'. He was the only vampire that the Sika Madu was interested in. When he was imprisoned by the rebels in dark ages of ancient Greece, Sika Madu visits him with a bought slave named Yu and assures his safety with him. Sika Madu was very kind to Ashera being almost as a parent to him .
Now being named the demon Shikama Doji, he enters his mind and tells him that that Asuramaru isn't a demon calling him with his original name, Ashera Tepes to remember him, even though Asuramaru treats him coldly such as annoyed at entering his mind and even fighting him, Shikama Doji telling him he is glad he's been doing well. He forces Asuramaru to remember his past life, what was done to him and who he used to be, as he remembers walking with his sister Krul before being saved by Yu. Shikama Doji tempts him and Yu about their memories but Asuramaru doesn't care about the past and simply states that he looks scary.
In the Dark Ages of Greece Ashera was along with Noya, in that time they were just acquaintances, although their relationship seemed strained in that Ashera seems to be uncomfortable with his ruthlessness and willingness to kill Yu. However in the present, he seems to be interested in Ashera when he found him in Yu's sword, seeing it as where he ran off to. Asuramaru, with just remembering him slightly, considers him a serious threat, even being willing to voluntarily give Yu more power to escape from Noya.