Doppo Kunikida vs. Ryūnosuke Akutagawa

Doppo Kunikida vs. Ryunosuke Akutagawa is a battle fought between Armed Detective Agency member Doppo Kunikida and the Port Mafia's attack dog Ryunosuke Akutagawa during the investigation of the serial disappearances of Yokohama visitors.

It occurred somewhere in the Port of Yokohama when Kunikida and new Agency hire Osamu Dazai were questioning their cabdriver, the culprit behind the abductions of the case victims.

Prologue
After Kunikida and Dazai fail to save the Yokohama visitors at the abandoned hospital, Kunikida deduces that their cabdriver is behind the kidnappings. As they ride his taxi and question him, the cabdriver confesses his crimes, albeit asking the detectives to grant him 72-hour protection, particularly from the Port Mafia with whom he explains having aggravated in the organ-trafficking business using his recent abduction method. Suddenly, the Mafia arrives and shoots at the taxi, causing the cabdriver to flee out of fright.

Dazai storms out to chase the cabdriver amidst Kunikida's apprehension, compelling him to activate his ability and materialize a stun grenade to quell the mafiosi shooting. Whilst disoriented, the mafiosi are fended off by Kunikida in physical combat.

Battle
Kunikida suddenly senses some bloodlust from behind him, and a black torrent runs past beside him that slices through the taxi, splitting it in half. Kunikida immediately kicks off the ground to evade it and rolls across the ground. He then sees a man clad in black coughing from a distance, whom he thinks must be the source of the bloodlust.

Kunikida expresses knowledge on the man approaching him, who turns out to be Akutagawa, infamously referred to as the Port Mafia's Hellhound among many other aliases. As Akutagawa asks where the cabdriver is, Kunikida directs him to his direction, though he capriciously refuses to let the mafioso kill their witness. Akutagawa sends a black rain of Rashōmon that pierces all around Kunikida's body. In retaliation, the latter manifests a wire gun and shoots at Akutagawa, but the mafioso's Devoured Space deflects it. Rashōmon instantly morphs its head, whose fangs tear into Kunikida's left shoulder, forcing him to retreat. Akutagawa sends another barrage of attacks on Kunikida, who struggles to dodge all onslaughts.

As Kunikida lands on a paved road, Akutagawa sends a fountain of spears to the air as distraction; a blade pierces through Kunikida from the ground and slowly wraps his neck to lift him from the ground. It then shoves him at the wall and gradually strangles him. Kunikida shoots his wire gun at the water pipe behind Akutagawa, which showers the latter with water. Kunikida instantly materializes a stun gun from his notebook and tosses it at the puddle of water with the drenched Akutagawa, electrocuting him. Kunikida is soon released from Rashōmon's grip.

Aftermath
After receiving the shock, Akutagawa amusingly retracts his earlier tirade towards the Agency, while Kunikida challenges him to resume their battle if he wishes so. Akutagawa acknowledges his offer to see whether Kunikida has what it takes to kill him, but he notes the incoming police approaching nearby. As such, Akutagawa withdraws and assures Kunikida that they shall continue their bout in another time.

After the mafioso casually leaves the area, Kunikida falls to his knees, hoping Akutagawa never returns. Kunikida soon takes a short respite and reports the incident back to the Agency. He also has his wounds temporarily tended to in the Agency infirmary and heads to the office, where Dazai reports having caught the cabdriver and handed him off to the police.

Light Novel and Anime Differences
The anime relatively shortens the battle, minimizing Akutagawa's attacks on Kunikida. Hence, the detective receives minor injuries and wounds compared to the intensity of the battle in the light novel. To illustrate, in the anime, when Akutagawa slices through the taxi, the vehicle explodes that sends Kunikida flying backwards. Akutagawa then unleashes various attacks on Kunikida, while the latter manages to fend off against Rashōmon by shooting at its tendrils. He almost immediately shoots the water pipe behind Akutagawa using a pistol rather than a wire gun, with the mafioso not having used his Devoured Space against Kunikida's shots. Afterwards, Kunikida electrocutes Akutagawa using his stun gun by tossing it at the puddle of water with him.

Since the light novel takes place during Dazai's entrance to the Agency, Kunikida and Dazai are not aided by Atsushi Nakajima, who accompanies them in the anime. Furthermore, Akutagawa is implied to not have yet known that Dazai is employed in the Agency in the light novel, as he sets out to find him after the Azure Apostle incident has been concluded. This is modified in the anime when Akutagawa remarks how the Agency is apparently worthy of being Dazai's cover, indicating that Akutagawa knows of Dazai's membership in the Agency.