The Eternity Devil arc is the 3rd arc of Chainsaw Man and spans from chapters 14 to 22. It follows our main group of Devil Hunters as they arrive at a hotel in hopes of finding a piece of the Gun Devil.
In order to build motivation among them, Himeno makes a promise to kiss the person who kills the devil in the hotel which does wonders for Denji as he charges ahead to search for it while Arai, who also shows interest in Himeno, competes with him. While they’re searching along with Kobeni and Power, we get a peek into the past between Aki and Himeno as she asks him not to die due to 5 of her partners dying before due to their lack of ability.
After killing a small devil with the appearance of a head, the group proceeds on inspecting the hotel. However, they notice that they stay on the same floor even while trying to go up or down and soon conclude that they are stuck on the 8th floor due to the power of a devil which has made them enter a sort of loop.
We see all the members, especially Kobeni panicking and making the situation more anxious through her breakdown. Denji on the other hand is satisfied that they can sleep how much ever they want and takes a nap.
While everyone tries to pass the time, we get further insight into Aki and Himeno’s backstory as she tells us how she taught him to appreciate cigarettes as well as how their relationship progressed. Back in real-time, we are finally introduced to the Eternity Devil who says that he’d let them go if they gave him Denji.
Kobeni tries to take him up on his offer but is stopped by Himeno. She then tries to beat the Devil using her Ghost Devil but ends up failing. As the Eternity Devil keeps getting bigger and everyone is enveloped by fear, even Himeno as she does not want to lose Aki, Denji decided to jump into the belly of the beast and try fighting it.
He falls into the Eternity Devil’s mouth and starts cutting everything up with his chainsaws. To counter his damage and loss of blood, Denji also begins drinking the Blood of the Devil so he can recover using his hybrid powers. Finally, after 3 days of continuous pain, the Eternity Devil begs Denji to kill him and is landed the finishing blow.
After escaping the hotel, the group meets up for drinks later. We see everyone having a jolly time and interacting with each other. Himeno then reminds Denji of his reward, but in a disgusting moment that no one expected, she ruins his big moment by throwing up in his mouth due to the several drinks she had before.
After spending the rest of the night in the toilet and passing out, he woke up at Himeno’s house with a pleasant surprise as she was kissing him but this time instead of vomit, she gave him water. Then when she asks him if he wants to go all the way, he gets reminded of Makima and decides not to.
The next morning, they have breakfast together while deciding on a pact where Himeno would help Denji get together with Makima in exchange for his help in getting her together with Aki. In the final moments of the arc, we are shown Makima and her group traveling to Kyoto by train before getting ambushed and shot by the Gun Devil’s henchmen.