Justice Devil

The Justice Devil (正義の悪魔) is a Devil that embodies the fear of justice. He is the secondary antagonist of the War Devil arc.

Appearance
The Justice Devil’s true appearance is unknown but the Class President’s transformation takes a form of a disfigured blob of flesh with human lower torso and legs, that possesses large muscular tentacles with claws-like fingers, which are sharp enough to cut through human flesh and bones. It also has six heads, two of which are merged, with different expression of their host.

History
At some point, the class president made a contract with Justice Devil for an unknown price, because she was jealous of her classmate, Asa Mitaka for capturing Mr. Tanaka's attention due to her aloofness, and the lack of socialization in their class. Mr. Tanaka was also having an affair with the class president, but it's unknown when it started.

War Devil arc
After Asa accidentally killed Bucky, the class president and Mr. Tanaka decided to walk with her to his grave at night in hopes the spirit of him would've forgive her for killing him.

On the way there, Mr. Tanaka, and the class president cross the street, and Asa stays behind. The class president realizes it's because Asa won't cross the street without the green traffic signal and begins to berate her for it for being a goody-two-shoes. She suddenly mutates into a being made of muscles and reveals that she made a contract with the Justice Devil, claiming that she and Mr. Tanaka had been having relations, but he had a thing for her, which held them back. Because of this, the only way for them to be happy is to kill her. She also reveals that her plan was for Mitaka to kill Bucky in order to humiliate her.

The class president is later killed alongside with Mr. Tanaka by the War Devil after it took Asa's body. Later, Yuko made a deal with the Justice Devil, which allowed her to read Asa's mind.

Abilities
As a Devil, the Justice Devil possesses all of the standard devil abilities. These include the ability to make contracts with humans. The contracts with it seen so far are those with the class president and Yuko for an unknown price.

Devil Powers

 * Justice Empowerment: The Devil Justice can turn anyone's sense of justice into a contract with him into power. This power seems to vary according to the sense of justice who made the pact:
 * The contract with the class president, who wished to have a happy ending with her teacher, gave her the power to transform her body into a blob of flesh with multiple heads, large muscular tentacles with claws-like fingers and superhuman strength. While in her transformed state, she is able to move very quickly, being able to attack in just seconds and she was capable to slice though Asa Mitaka's skull and flesh, killing her instantly. It is unknown if this transformation is an extension of the devil himself or a specific upgrade granted to the class president.
 * The contract with Yuko instead gives her the ability to read others' minds and detect their inner thoughts and feelings.

Trivia

 * The Justice Devil could be based more on one one’s own personal sense or “idea” of justice rather than actual justice itself. The transformation of the class president shows numerous heads, as if to symbolize that the idea of justice has "many faces", varying according to each person's personal perspective.