Port Mafia Arc

The Port Mafia Arc (ポートマフィア編,) is the first story arc in Bungo Stray Dogs.

Synopsis
It showcases the protagonist, Atsushi Nakajima, as he adapts to live with his ability and meets both the Armed Detective Agency and Port Mafia, becoming the epicenter of their latest conflict.

Man-Eating Tiger at Yokohama
A young orphan is seen starving beside a river and decides to steal money from the next man who passes by. However, he sees a drowning man and saves him. It was then revealed that the drowning man is attempting to commit suicide but is saved by the orphan. As the drowning man wanted a clean suicide and the orphan was entangled to it, he offers to buy him a meal using his coworker's money who just arrived at the scene looking for him. The drowning man's name reveals to be Osamu Dazai and the orphan's name is Atsushi Nakajima.

Later at a soba restaurant, Dazai and his coworker Doppo Kunikida reveal to be detectives from the Armed Detective Agency, a detective company with ability users who is currently seeking a case about a man-eating tiger. Shocked by what he heard, he tries to run away but is restrained by Kunikida. Atsushi tells them that he knows the tiger as it is the one who cause wreckage to the orphanage where he came from and followed him until Yokohama. Shortly after, Dazai offers Atsuhi to join him in their tiger hunt as it has compensation.

At the warehouse, Dazai and Atsushi are seen waiting for the tiger to appear. As the moonlight appears, Atsushi panics as the tiger will appear soon. Dazai tells Atsushi that it is not a coincidence that the tiger appears just as where Atsushi is and reveals that Atsushi is an ability user who can transform into a tiger. Atsushi eventually transforms and attacks Dazai but Dazai nullifies it. Shortly after, the other agency members including Ranpo, Yosano, and Kenji arrive at the scene.

Atsushi's Entrance Exam
After being taken by the agency, Atsushi receives a call from Dazai and meets up with him. Dazai tells Atsushi that he is about to secure a work him. Just then, Kunikida finds them and immediately informs them about a bomber holed up in the agency.

Dazai, Kunikida, and Atsushi soon arrive at the agency. Kunikida tries to confront the bomber in attempt to save the hostage however the bomber knows Kunikida's identity. While Atsushi and Dazai are hiding from sight, Dazai tells that the bomber may have an issue with the agency and his appearance will only cause more harm. As a result, Atsushi is the one who approaches the bomber trying to stop him and making him surrender. Due to the distraction, Kunikida manages to activate his ability and restrain the bomber.

The timer on the bomb stopped but someone had pushed Atsushi causing the timer to start again. Panicking and not sure what to do, Atsushi covers the bomb with his body. After the bomb reaches to zero, it didn't explode. It is revealed to be Atsushi's entrance exam to the agency. Shortly after, the president appears and leaves the decision whether Atsushi passed the exam to Dazai. Dazai then welcomes Atsushi to the agency.

Port Mafia's Appearance
[[File: The other agency members introduce themselves. The disguised bomber reveals to be [[Jun'ichirō Tanizaki]] and the hostage is his sister, Naomi. Atsushi asks the members what their job is before joining the agency. The Tanizaki siblins are both students, Kunikida formerly taught mathematics at a licensed school. However, Atsushi can't guess Dazai's job to which Kunikida describes Dazai's prior vocation is one of the great mysteries of the agency.

Shortly after, the agency receives a client request to investigate something. The young woman states that there are people of low character hanging out behind their building. Kunikida gives the job to Atsushi, accompanied by Tanizaki whose sister also decides to tag along. Before the stakeout, Kunikida gives a picture of a young man to Atsushi and tells to never encounter the person., if he does, he must flee. Kunikida reveals the young man's name to be Akutagawa, one of Port Mafia's attack dogs.

Meanwhile at a police station, Akutagawa delivers a case and kills the policemen. After leaving, a woman enters the station and sees the policemen dead. Soon after, the police station explodes and Akutgawa is seen talking to someone over the phone asking what's the next order.

The client soon leads them to the company building however Tanizaki finds the place suspicious and asks if it is really the place. The young woman introduces herself as Higuchi and tels them that her real goal is to get all of them. She speaks to Akutagawa through phone telling that she have captured them.

Higuchi proceeds to shoot them. Naomi manages to save Tanizaki by shielding her body against him. As a result, Tanizaki panics and tells himself that he needs to get Naomi treated. Just then, Higuchi corners him pointing a gun to his head. While carrying Naomi, Tanizaki acitivates Light Snow. Unable to pinpoint Tanizaki form the snowfall, Higuchi is strangled by Tanizaki from behind. However, just then Akutagawa comes to Higuchi's aid and attacks Tanizaki.

Akutagawa introduces himself to Atsushi and reveals that their goal is to capture Atsushi alone.Akutagawa activates Rashōmon and attacks Atsushi. Atsushi and Akutagawa engage in a battle - with Atsushi turning himself into a tiger.

In the middle of their battle, Dazai appears and nullifies both of their abilities. It is revealed that Dazai had put a bug, an eavesdropping device to Higuchi and saw through her whole plan. Akutagawa declares that they will retreat for now but will return to capture Atsushi once more. Dazai asks their reason for capturing Atsushi and Akutagawa reveals that Atsushi has a reward of 7 billion yen on the black market. It is then revealed that Dazai is an ex-mafia.

Impact

 * Atsushi Nakajima discovers his ability and joins the Agency.
 * The Armed Detective Agency is introduced.
 * Port Mafia is introduced.
 * Dazai's past occupation as a member of the Port Mafia is revealed.
 * Atsushi Nakajima and Ryunosuke Akutagawa develop their rivalry.
 * The rivalry between Osamu Dazai and Chūya Nakahara is introduced.
 * Kyōka Izumi defects from Port Mafia.