Eternity Devil

At its center the Eternity Devil is a knot of flesh bent into a figure eight, a shape that doubles as the infinity sign, with an eye and a mouth set at each loop and a further pair of mouths between them. Sealed inside the space it rules, it swells into a churning tide of arms and heads grafted together, a mass that begins almost laughably small and frail before ballooning at speed.

Its reborn form looks nothing like the first. When Asa wrenches its trap apart, what remains is a roughly human shape built from half-melted fingers, topped by a featureless hooded head and gliding along on a single slug-like foot. The gulf between the two versions is usually chalked up to the original having gorged on Gun Devil flesh, an unnatural boost the second one lacks.

Cruelty delights it. The devil cackles at Kobeni's terror as she falls apart and is knocked out cold, and it freely dangles bargains in front of trapped humans whenever doing so serves its ends. The incarnation that crawls back from Hell adds a short fuse to the mix, spitting curses at Fami once their scheme collapses and sneering at Asa for imagining that a single million yen could buy an aquarium.

The devil's signature trick is to take a single floor of a building and warp it into a looping pocket of space from which no direction leads out, a sealed expanse that effectively becomes its stomach. Time halts inside, every clock locked at 8:18 with the second hand snapping back each time it ticks forward, while the repeating rooms can starve captives or, turned to advantage, hand them limitless food, water, and cash. Within the trap it grows a ravenous avatar that starts tiny and balloons in power until it can shred even a transformed Denji.

Its first campaign comes when a six-person Special Division 4 squad enters a hotel to put it down after it fed on a hunk of Gun Devil flesh. The squad reaches the eighth floor, finds itself sealed in the time-stopped loop, and watches the devil bloat across the corridor. It offers freedom in trade for feeding Denji to it; Kobeni's attempt to comply is stopped, Aki cannot call up the Fox Devil, and Himeno's Ghost arm only wounds and enrages it. Realizing the thing fears his chainsaws, Denji throws himself into its mouth and rips his cord. The brawl drags on for roughly three days, the devil tearing him apart while he drinks its blood to keep going and Himeno yanking his cord to revive him after his neck snaps. Worn down by the endless slicing, the devil at last surrenders its core and begs to die, and Denji halves it.

It resurfaces in the Dating Denji arc, teaming with Fami to pressure Asa into weaponizing Denji. Hiding inside the aquarium where the pair are on a date, it reshapes the building into a hallway with no exit and slowly unhinges the Devil Hunter Club, sparing only Denji, Asa, and Yoshida. Asa gathers more than a million yen from the looping rooms and reforges the whole aquarium into the Aquarium Spear, freeing everyone trapped within. The devil reveals itself and lashes out, but Yoshida lops off one of its hands with the Octopus Devil, and Yoru, back in control of Asa's body, runs it through with the spear.