US president gives orders to 20% of the gun devil to kill Makima. so for the countermeasures Makima summoned Aki Hayakawa, Power and Denji to lead on this mission to defeat the gun devil. Aki Hayakawa was contracted with a future devil before this event. After the announcement of this mission, the future devil instantly warned Aki hayakawa If you accept to go on this mission, then you will be killed by Denji.
So Aki Hayakawa first refused to go on this mission. But Makima have some other plans, she make a strong objection of this matter, and forced Aki to be the part of this mission. the guns devil appears in a forest near to city. Makima arrived there and killed the gun devil by using the other devil hunter's devil power by controlling them with the control devil of her. Denji and Power was not the participants in this battle of Makima vs Gun devil but Aki Hayakawa was. when Makima summoned a dimentional powerful devil to kill gun devil, sametime a gun devil's flesh contracted with Aki Hayakawa, and he becomes the Gun Fiend devil.
After defeating the gun devil, Makima inform Denji that Aki Hayakawa is become Gun fiend like power the blood fiend and he is at the gate. Denji tells power to ran away from the window, Denji opens the door, He thinks that Aki will recognize him and do not attack on him. But within the door opened Aki the Gun Fiend attacks on the Denji. The duel started in the street. before this duel and the door opened. Denji told power to ran from here with her pet. but power get caught in this duel fight of Denji nad Aki Hayakawa. Aki pointed the gun towards Power, Denji Got angry at this act of Aki, and says I was never wants to face situation like this.
Denji once again raised and starts attacks on the Aki. But his attacks merely landing on the gun fiend. at last he fall down, Aki thinks Denji is died and he starts moving to the opposite direction of the Denji. Sametime some people came there and give him some blood of his own. Denji stands once again and killed Aki hayakawa with his chainsaw from the behind. At the sametime The Future Devil appears there, who had the contract with the Aki Hayakawa, He said I warned you earlier stay away from the mission of Gun devil.