Eternity Devil

The Eternity Devil (の) is a devil that embodies the fear of eternity. It is the primary antagonist of the titular Eternity Devil arc and later the Dating Denji 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.

Second Incarnation
After its death, the Eternity Devil returned to Earth with a different appearance. When its effect is forcefully ended by Asa turning the aquarium into a spear, the Eternity Devil appears as a vaguely humanoid mass of partially melted fingers with a hood-like head with no facial features and instead of legs it has a slug-like foot. It appears to be far removed from the encompassing Devil it was before.

The differences likely stem from the previous incarnation being abnormally powered-up through eating Gun Devil flesh.

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

It's second incarnation additionally has a quick temper, cursing out Fami after their plan backfires.

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 it's heart is not located on the eighth floor and that they're in its stomach so that there is no way for them to kill it.

Kobeni and Arai panic and their increasing fear fuels the Eternity Devil's growth as it chases Denji, Aki and Himeno. It 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. It offers up its core to Denji, begging for death and Denji obliges by cutting it 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.

After Asa turns the aquarium into a spear and releases its inhabitants from the Eternity Devil's captivity, the devil appears in the open. Cursing Fami, whom it had made a deal with, it moved to attack Asa but had their hand torn off by the Octopus Devil. Yoru then reawakened in Asa's body and used the spear to kill the Eternity Devil.

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 building 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.


 * Looped Environment: The floor inside the Eternity Devil's stomach will lead to other identical rooms, creating an infinite loop of identical environments with the same elements. This can potentially lead to the death of those trapped within it from hunger or thirst, but also be used to their advantage, potentially being able to obtain food, water and money almost infinitely. Taking advantage of this feature, Asa Mitaka managed to collect over a million yen by collecting the money in the various repeating rooms.


 * 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.. Its second incarnation, however, doesn't display this kind of power. It is therefore unknown whether it can always use it or only after ingesting a piece of the Gun Devil's flesh.

Trivia

 * The Eternity Devil's rankings in the Popularity Polls are as follows:
 * The Eternity Devil ranked 64th in the First Popularity Poll with 64 votes.
 * 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.