Eternity Devil

The Eternity Devil (の) is a devil that embodies the fear of eternity. He is the primary antagonist of the titular Eternity Devil arc.

First Incarnation
The Eternity Devil's core is a lump of flesh in the shape of the number 8 which can also be seen as the infinity symbol with an eye and mouth on either side and two mouths in the center.

Within its own stomach the Eternity Devil can manifest as an endless wave of flesh consisting of many arms and heads fused together. It initially appears very small and weak but rapidly grows over time.

Personality
The Eternity Devil finds amusement in the fear and suffering of others, openly laughing as Kobeni panics and is knocked out. He is willing to make deals with humans in order to achieve his objectives.

Eternity Devil arc
A six-man team from the Special Division 4 is sent into a hotel to kill the Eternity Devil who had eaten a chunk of the Gun Devil's flesh. As the group reach the eighth floor they encounter a disembodied head created by the Eternity Devil.

Power slices the head in two and the team realize that the head doesn't contain the Gun Devil chunk that they were looking for. The team continue onwards but quickly realized that they're trapped on the eighth floor with all of the rooms linked to each other and time stopped.

The body of the Eternity Devil which Power seemingly killed grows in size until it blocks off a room and section of corridor. As Denji, Aki Hayakawa, Himeno and Power stare at it in confusion, it offers to make a contract with them, stating that it will release them if they feed Denji to him.

Kobeni attempts to kill Denji to accept the Eternity Devil's offer but she is incapacitated. The Eternity Devil laughs at her, and Aki tries to summon the Fox Devil over it but is unsuccessful. Himeno uses her Ghost Devil arm to wound the Eternity Devil but she merely enrages the devil who grows larger. The Eternity Devil reveals that his heart is not located on the eighth floor and that they're in his stomach so that there is no way for them to kill him.

Kobeni and Arai panic and their increasing fear fuels the Eternity Devil's growth as he chases Denji, Aki and Himeno. He begins tilting the hotel's floor and demands Denji's heart while boasting that their deaths are assured.

Denji realizes that the Eternity Devil is seemingly afraid of his chainsaws since it is trying indirectly to kill him, and that it felt pain from Himeno's earlier attacks. Denji jumps out of the room he was in and lands straight in the Eternity Devil's mouth, pulling his cord to activate his transformation.

The Eternity Devil and Denji fight each other, the Eternity Devil causing severe injuries with its many arms and heads but Denji drinks the blood from the Eternity Devil's wounds in order to resupply his dwindling reserves of blood. At one point the Eternity Devil manages to snap Denji's neck but Himeno uses her ghost arm to pull Denji's cord again and make him regenerate.

After roughly three days of nonstop fighting the Eternity Devil breaks down from the torture of being repeatedly sliced by Denji's chainsaws. He offers up his core to Denji, begging for death and Denji obliges him by cutting him in two.

Dating Denji arc
After Fami tells Asa Mitaka that she cannot leave the aquarium she was on a date with Denji at until she turns him into a weapon, Denji assumes the Eternity Devil has returned from Hell. As such, the aquarium has become endless, much like the eighth floor of the hotel.

Abilities
As a Devil, the Eternity Devil possesses all of the standard devil abilities.

Devil Powers

 * Pocket Reality Creation: The Eternity Devil could turn an entire floor of a hotel into a looped section of 3-dimensional space, making escape in any direction impossible. This section of space effectively becomes the Eternity Devil's stomach.
 * Time Stop: Inside the devil's stomach time is effectively stopped due to being cut off from the rest of the world. All of the clocks inside the devil's stomach showed at the time as being 8:18 as the second clock always reverts back to its original position.
 * Avatar Creation: The Eternity Devil can create a monstrous body inside of its stomach that will hunt down and try to kill anyone inside it. This body starts off small but exponentially grows in size. The Eternity Devil's avatar possess a great deal of physical power, being able to tear Denji's body apart even after his transformation and cause significant blood loss.

Trivia

 * The recurring appearance of 8 (Special Division 4 being trapped on the 8th floor with time frozen at 8:18) is due to 8's visual similarity to the lemniscate (∞), the infinity symbol. This is a reference to eternity (the state of being everlasting, i.e infinite), the embodiment of the Eternity Devil.
 * Similarly, the Eternity Devil's core resembles a lemniscate.
 * The Eternity Devil's appearance somewhat resembles that of the Sea God, a monster that appears in the Berserk manga.