Atsushi Nakajima, Ryūnosuke Akutagawa, and Kyōka Izumi vs. Tatsuhiko Shibusawa

Atsushi Nakajima, Ryūnosuke Akutagawa, and Kyōka Izumi vs. Tatsuhiko Shibusawa is a battle fought between Armed Detective Agency members Atsushi Nakajima and Kyōka Izumi and Port Mafia member Ryūnosuke Akutagawa against the Tatsuhiko Shibusawa, also known as the Collector, who is responsible for the Yokohama fog incident.

It happened in the ruins of Skull Fortress somewhere in the Yokohama Settlement, after Fyodor Dostoevsky craftily revives Shibusawa, granting the latter draconic powers as an ability-like life-form. This rebirth compels Atsushi, Akutagawa, and Kyōka to collaborate in defeating Shibusawa permanently.

Prologue
Shibusawa and Atsushi are able to peer into their shared past six years ago, when Shibusawa tortured Atsushi in the orphanage, whom he was told by Fyodor to possess the ability that "guided the envy of all ability users". However, Atsushi transformed into the white tiger back then and killed Shibusawa. With their memories finally vivid once more, Fyodor revives Shibusawa from the singularity using his skull and red crystal as its vessel, granting him draconic appearance and powers.

Battle
Akutagawa and Kyōka manage to locate Shibusawa in the dilapidated Skull Fortress and activate their respective abilities. Shibusawa becomes amused how two ability users like them are able to take back their separated abilities. Clad in Tenma Tengai, Akutagawa launches a punch through Shibusawa's torso, but to no avail. Demon Snow strikes at Shibusawa, and Akutagawa rushes to attack once more, only for Shibusawa to simultaneously block their offenses efficiently.

Pondering about his past and his connection to the tiger, whom he realizes has kept him alive ever since, Atsushi finally makes amends with the tiger and regains his ability back. Back on the battlefield, Shibusawa overwhelms both Akutagawa—with Tenma Tengai having reached its limit and reverting into his overcoat—and Demon Snow. Shibusawa then summons claws to strike Kyōka, but Atsushi, transformed as the tiger, pierces a trail of light through the ground between the two.

Shibusawa soon realizes that he must be the dragon, the true form of the chaos of abilities as told by Fyodor, while Atsushi must be the tiger, the one resists all abilities. He asks Atsushi whether he is to kill him again, much to Kyōka's and Akutagawa's surprise. Atsushi merely retorts that he has come to put something back where it belongs, which Shibusawa acknowledges.

Atsushi leaps towards Shibusawa and knocks him away. As he chases the latter, Shibusawa leaps forward and pounds him with both closed fists, then, grabbing him by the feet, plummets him to the ground. Atsushi quickly buries his fist in Shibusawa's face, but he gets kicked away by Shibusawa. Akutagawa launches twin beast-headed Rashōmon tendrils at Shibusawa, but the latter grabs both fabrics and tosses them with Akutagawa into the air, afterwards hurling them to the ground.

Demon Snow strikes Shibusawa with its katana, but he defends himself with his scale-like forearm and punches the ability off him. Shibusawa kicks it away and separates it from Kyōka, who is also sent flying towards an upright slab nearby. Before she can directly take the impact, Atsushi instantly takes cover for her. He then urges the three of them to work together in order to save their city, which Akutagawa later agrees to. Atsushi asks Kyōka to call Demon Snow, though she grows visibly frightened.

Atsushi promises Kyōka that Demon Snow would listen to her call and returns to battle Shibusawa in physical combat. After getting punched away, Atsushi launches a counterattack which Shibusawa evades by floating up in the air. Kyōka then activates Demon Snow, which materializes behind Shibusawa and pins him down with her katana. Akutagawa then turns Rashōmon into various blades to encage the pierced Shibusawa inside. Atsushi then leaps inside Rashōmon's enclosure and launches various quick attacks towards Shibusawa, who becomes elated at the feeling of his death.

With Atsushi charging at him, Shibusawa counters with his horn-like crystal on his forehead and shoots a beam that destroys the Rashōmon cage and encloses the two of them instead with a red haze. As Akutagawa and Kyōka get blown away, Shibusawa manages to unearth Atsushi's blue ability crystal and reaches out to steal it. Atsushi, correcting him that the crystal is not merely an ability but himself, reaches out similarly to retrieve the crystal. In the end, Atsushi takes hold of the crystal and regains his tiger ability.

In a final stand, Atsushi attempts to crush Shibusawa's skull, which causes the two of them to lock fingers. As their powers clashed, Shibusawa's horn gradually cracks, and his body slowly disintegrates. He finally understands that what their encounter was for and that Atsushi is the angel who would save him. His horn that houses the crystal gets destroyed, leaving behind only his skull, which Atsushi crushes with both his hands. A pale blue light then engulfs the red haze swirling around them, and the light swallows the red fog that looms over Yokohama until it completely fades.

Aftermath
At daybreak, Atsushi smiles back at Kyōka with victory, while Akutagawa silently leaves; he soon finds Chūya Nakahara completely weakened but now conscious following his battle with the dragon and presumably takes him back to their headquarters. Osamu Dazai approaches Atsushi and Kyōka, seemingly to explain his earlier actions, but Atsushi immediately interrupts and claims that he was only trying to protect the city and save others, much to Dazai's shock and later amazement. They also find the rest of the Agency safe, much to their relief.

Meanwhile, after Shibusawa's defeat, the Special Division for Unusual Powers detect the disappearance of the singularity and the red fog, also learning that the Order of the Clock Tower has aborted their supposed mission to incinerate Yokohama to end the incident. Over the course of various days after the incident, their agenda involves the cover-up of the event, documented as the "Dead Apple" incident.

Film-Light Novel Differences
During the early part of the battle, the light novel mentions Demon Snow's katana being snapped in half by Shibusawa, though the film does not portray this. In the film, after Akutagawa's Tenma Tengai reverts to his overcoat, Shibusawa kicks him away and punches Demon Snow consecutively. This quick instance is expanded in the light novel: Shibusawa immediately attempts to impale Akutagawa after slamming him to the ground, but Demon Snow intervenes. Shibusawa, however, anticipates this and deflects its blade, afterwards kicking Akutagawa away. Before he punches Demon Snow, he is also noted to pretend lowering his guard to lure Demon Snow to him.

In Atsushi's and Shibusawa's initial clash, after Atsushi sends him flying with a punch, the film portrays Shibusawa grabbing Atsushi's feet and hurling him down the ground afterwards when they charge at each other. This seems to be omitted in the light novel, as it cuts straight to Atsushi punching Shibusawa in the face, which happens only soon after in the film.

Afterwards, in the light novel, Shibusawa calls Akutagawa weak when the latter attacks using Rashōmon and also jeers at Kyōka's repetitive tactics in using Demon Snow, though he does not specifically say anything during this instance in the film. Moreover, Shibusawa uses his claws to tear through Demon Snow in the light novel, while he attacks with a sharp kick that sends Kyōka flying and causes Demon Snow to dissipate.

When the trio resolve to fight together rather than individually, the film portrays their collaborative effort to trap Shibusawa with Kyōka resummoning Demon Snow upon Atsushi's call. However, the light novel depicts Atsushi and Shibusawa clashing in a prolonged period of physical combat, compelling Kyōka to reactivate Demon Snow to help Atsushi, whom she observes to be at a disadvantage.

Later, inside the Rashōmon cage, the film portrays Shibusawa halting Atsushi's onslaughts seemingly due to his draconic aura, while the light novel depicts Shibusawa sprinting towards and kicking Atsushi in the chin to stop him. When their fingers lock during the climax, the light novel mentions that Shibusawa's facial scars glow before he disintegrates and turns into a skull, though the film does not portray this.