Gun Devil

The Gun Devil (銃の悪魔, Jū no akuma) is a very powerful devil who embodies the fear of guns.

Due to its overarching role in the story, it can be considered to be the primary antagonist of the series.

Appearance
Chunks of its discarded flesh resemble bullets.

Personality
The Gun Devil's personality is currently unknown.

History
Thirteen years before the present day, the whole world tried to cash in on guns as a countermeasure against devils. This led to an increase in gun use during crimes and civil revolts. Due to heavy media coverage of gun crimes in every country, worldwide fear of guns has increased drastically.

On November 18 a large terrorist attack involving guns occurred in America, causing that to be the day that the Gun Devil first appeared. The Gun Devil hit Japan for 26 seconds, killing 57,912 people. Aki Hayakawa witnessed the Gun Devil destroying his house and killing his family as it passed by. It hit several countries around the world in succession eventually leading a death toll of 1.2 million lives in only five minutes. After that the Gun Devil disappeared but its impact on human society led to an overall increase in fear in all devils.

Aldo, Joey and their brother survived the Gun Devil's attack but lost their home along with their father, mother and grandmother. This would one of the events in their lifes that would lead them to believe that they're immortal.

Bat Devil arc
Makima asks Denji for a favor; she wants him to defeat the Gun Devil whose location is currently unknown. She offers to grant any one wish he has if he can kill it.

Makima explains the history of the Gun Devil to Denji and explains that they're currently trying to track it using pieces of the Gun Devil's flesh. Meanwhile Aki and Himeno take down a devil and recover a chunk of the Gun Devil's flesh from it. The pull of the Gun Devil's flesh leads them to Morino Hotel where they dispatch a six-man team to investigate.

Eternity Devil arc
A piece of the Gun Devil's body is recovered by Aki from the Eternity Devil's corpse. Later at a party Aki comments that devils with Gun Devil pieces are becoming more common.

Katana Man arc
The Katana Man confronts Denji, Aki, Himeno and Power in a restaurant and relates a story to them about his grandfather. As he finishes up, he tells Denji that the Gun Devil wants his heart and opens fire, wounding Denji, Aki and Himeno. Simultaneously most of the members of the Special Divisions elsewhere are assassinated.

After learning from Madoka that most of the humans in Special Divisions 1, 2, 3 and 4 have been killed in coordinated gun attacks, Makima states that it is likely the Gun Devil is involved.

Bomb Girl arc
Beam tells Aki that the Bomb Devil is the ally of the Gun Devil. When pressed on how he knows this Beam claims that if he reveals this information that he will be killed and that he promised Makima to keep it secret.

Physical Abilities
Immense Speed: The Gun Devil is incredibly fast, able to kill 1.2 million people in various countries across the world in five minutes. Its speed is so great that pieces of its flesh burned off of its body as it moved.

Supernatural Abilities
Devil Empowerment: When devils of any type consume pieces of the Gun Devil's flesh, their power is greatly enhanced.

Regeneration: The Gun Devil's separated body parts fuse together when touching and will attempt to rejoin the Gun Devil's main body to regenerate.

Blood Consumption: As a devil, the Gun Devil should be able to restore its health by consuming blood.

Revival: As a devil, the Gun Devil should revive in Hell after being killed effectively making it immortal.