Armed Detective Agency vs. Black Lizard

Armed Detective Agency vs. Black Lizard is a battle fought between members of the Armed Detective Agency and Black Lizard operatives, the Port Mafia's assault unit, upon orders of Ichiyō Higuchi.

It happened as a raid operation by the Black Lizard in the Agency office primarily to prevent any more interference in their bounty hunt for Atsushi Nakajima, unlike their previous attempt on their target.

Prologue
After barely surviving an abduction attempt on his life by the Mafia, Atsushi turns anxious that he has placed the Agency in considerable danger. He further gets apprehensive after witnessing a crime scene that was performed by the Black Lizard, whom he hears from others is the Mafia's ruthless operational force. Wishing not to put them in harm's way especially from the Black Lizard, Atsushi decides to leave the Agency. He then contacts Higuchi and taunts her to capture him alone.

Higuchi assembles the Black Lizard to eliminate the Armed Detective Agency in order to prevent any other possible support that the weretiger might get again, similar to how Osamu Dazai previously interfered in their latest operation. In addition, she is unable to accept defeat at the hands of the Agency, mainly filled with anger for having Ryunosuke Akutagawa fail his mission.

Battle
Black Lizard commander Ryūrō Hirotsu gathers his deputy commanders Gin and Michizō Tachihara together with their respective squads to launch a raid at the Agency office. The Mafia pries the door open, and Hirotsu jeeringly apologizes for failing to book an appointment with the Agency.

Along the way, Atsushi hears gunshots coming from the direction of the Agency. Out of worry, he runs back to the office, only to find Doppo Kunikida flipping Hirotsu with relative ease and the unconscious beaten mafiosi (including Gin and Tachihara) piled up beneath Kenji Miyazawa, who calmly collects their machine guns. Meanwhile, Ranpo Edogawa and Akiko Yosano obliviously chat with each other at the side amidst the chaos, with Yosano even having a drink.

Aftermath
Kunikida reprimands Atsushi for running off out of the blue and directs him to help in the cleanup. Though he admits having been acquainted with raids, Kunikida expresses annoyance over the costly repercussions they have to manage, which he anticipates shall mess up their operation budget again. Kenji and later Yosano casually toss out the defeated mafiosi out the window as instructed by Kunikida. Atsushi then perceives the Agency as more terrifying and dangerous compared to the Mafia, afterwards crying out of implied relief.

Manga and Anime Differences
In the anime, Hirotsu blasts the Agency office door open with Falling Camellia, unlike in the manga where the mafiosi barge in to enter. Moreover, together with Kunikida, Kenji appears to participate in the fight alongside Yosano; Ranpo is the only one sitting idly drinking some Ramune. After they defeat the Black Lizard, Yosano reminds Kunikida to go around the neighborhood with apologies and gifts as they always do after the countless raids they have been receiving, further irking Kunikida.