Bungo Stray Dogs: Osamu Dazai and the Dark Era

Bungo Stray Dogs: Osamu Dazai and the Dark Era (文豪ストレイドッグス 太宰治と黒の時代,) is the second light novel of the Bungo Stray Dogs series, mainly focusing on Osamu Dazai's past in Port Mafia and telling the reason behind him leaving the organization.

Narrated through Sakunosuke Oda's perspective, the light novel consists of six chapters in total. Like its preceding light novel, Dark Era was adapted into the Bungo Stray Dogs anime, filling in Episode 13 to Episode 16 of the series.

Description
Before joining the Armed Detective Agency, Osamu Dazai was the youngest executive with the Port Mafia, the most notorious underground crime syndicate in all of Yokohama. When one of their colleagues suddenly goes missing, Dazai and fellow Port Mafia member Sakunosuke Oda are tasked with conducting an investigation… and at last, the reason why Dazai parted ways with the Port Mafia is revealed!

Summary
On their usual nightly gathering in Bar Lupin, Osamu Dazai, the youngest Port Mafia executive; Sakunosuke Oda, a low-ranking mafioso; and Ango Sakaguchi, a mafia intelligence agent talk about superficial thoughts and anything outside their professional lives. As they each share how their day transpired, Dazai recommends that they take a photo together, thinking that they shall not have any other chance to leave behind any evidence of the invisible bond they shared together in the bar. Indeed, as Oda narrates, that is the last time they can ever take photos together, as one of them dies soon after.
 * Prologue

The next morning, Oda is requested by mafia boss Ōgai Mori to locate Ango, one of Mori's valued members, who has gone missing since the previous night. Meanwhile, Dazai, veteran mafioso Ryūrō Hirotsu, and armed comrades arrive by the harbor, where one of their highly secured weapon armories was infiltrated by assailants carrying Grau Geist pistols, similar to men that Dazai's team has earlier fended off after stealing illegal goods. From the interrogation of the caught party, they come to know the group responsible, Mimic, whose emblem Dazai believes is the Grau Geist.
 * Chapter 1

Oda searches for hints regarding Ango's disappearance in his hotel suite, where he finds a small, hidden safe. At that instant, Oda is allowed by his ability, Flawless, to peer a few seconds in the future and let him evade a sniper shot from afar. After killing the assailant and his companion upon Dazai's intervention, Oda and Dazai unlock Ango's safe and find a Grau Geist pistol inside. Though Dazai tells Oda not to prematurely implicate Ango as a Mimic operative, Dazai infers that Ango had lied to them the previous night and asks Oda to take extra precaution from thereon in pursuing his search for Ango.

Out of habit, Oda eats some curry at Freedom Restaurant and visits five orphans who lost their parents from the Dragon's Head Conflict staying in the restaurant. Dazai arrives and reports new findings on Mimic, a foreign criminal organization of former soldiers expelled from Europe by an English organization. Dazai also surmises that the government's Special Division for Unusual Powers in charge of monitoring dangerous ability users in the country might be using Mimic's advances against the mafia to their advantage by having the two criminal groups kill each other.
 * Chapter 2

From his individual inquiries, Oda comes under the belief that Ango is a double agent who colluded with Mimic. After recollecting his and Dazai's first encounter with Ango at the mafia accounting firm, Oda perceives that the relationship among the three of them is starting to crumble. Later, Mimic operatives fall under Dazai's trap and get captured for questioning, but his apprentice, Ryunosuke Akutagawa, kills off the captured with his ability. Dazai berates Akutagawa out of irking and disappointment for taking out their remaining leads on Mimic.

Nonetheless, they manage to find a clue regarding the enemy's location, which traces back to an abandoned building. At Dazai's behest, Oda rushes to the place and finds Ango tied up in the place ridden with time bombs. After they barely escape from the explosion, Ango tells Oda about Mimic's gifted leader, André Gide, and warns him especially not to get in contact with the man. Oda later picks up a temari ball laced with poison, which turns out to be Ango's doing. The latter voices out his hopes to see him and Dazai at the bar again before leaving with the government's Black Special Ops Forces.

Oda recalls his past encounter with a middle-aged man when he used to read the penultimate part of a certain novel. The man advised him not to read the final part of the work and instead to write the ending of the novel himself. This advice compelled Oda from then on to become a mafioso who does not kill, in hopes of becoming a writer who writes about people's lives by the time he retires from the mafia.
 * Chapter 3

When he comes to, Oda reports the previous night's events to Dazai, while the latter informs him that the mafia executives have decided to utilize all their forces to face Mimic. Oda heads out to a surprise crossfire between the mafia's combat squad led by Akutagawa and Mimic operatives. He comes across Gide, and the two realize that they have identical, premonitory abilities. Thinking that Oda is the only one who can grant them a worthy end to their spectral lives despite Oda's refusal to kill anyone, Gide retreats with his comrades and warns Oda that he shall make him understand their plea.

At night, Oda and Dazai meet Ango in the bar like usual, though the three acknowledge that their relationship is now on the verge of a falling-out. With Dazai thinking that Ango is a triple agent from the Special Division sent to spy on the mafia and, later, on Mimic as a mafia member, Ango cautions Oda of the singularity phenomenon recently studied by the government. In the end, despite Ango hoping for their relationship to remain unchanged after all that happened, Oda and Dazai shut him out. He departs for good, only leaving behind the photograph they have taken with all three of them together.

Oda goes to a customs clearance company office that Dazai helped prepare for the orphans to stay in, but he is shocked to find the place ransacked. He soon finds the missing children abducted by Mimic in a bus and chases them. Though Oda manages to reach them, the Mimic driver sets the bus to explode, leaving the orphans dead. Ango facilitates a highly classified meeting between Mori and the Special Division director, Santōka Taneda. The Special Division requests the mafia to exterminate Mimic at all costs, which Mori accepts after acquiring a skilled business permit from Taneda as part of their deal. Oda heads to Freedom Restaurant, only to find the chef dead and a map that invites him to Mimic's base, after which Oda arms himself with his arsenal of weapons.
 * Chapter 4

Despite Dazai dissuading him from pursuing Mimic and in spite of a youth he stumbles upon warning him that he shall die if he continues down his course, Oda proceeds to his destination. He arrives in the building and kills off the soldiers with his skillful marksmanship and foretelling ability. Dazai apprehensively visits Mori and suspects him to be the mastermind behind recent events, which is an elaborate ploy all to acquire a skilled business permit from the Special Division. Mori says that he is correct, but he is confused about Dazai's apparent anger towards him when he merely claims to have done what is best for the mafia. Dazai tells him that Oda, whom he used as a pawn to achieve such a goal, is his friend, after which he rushes out to locate him.

Finally clashing with Gide in a singularity, Oda narrates that he decided to stop killing because he wished to become a novelist. He reckons that becoming a novelist requires one to sincerely understand how people live, the reason why Oda swore to stop killing. Later, Gide tells Oda that he and his soldiers inadvertently became criminals during the war until they became ghosts who wandered through the battlefield, seeking out the deaths they longed for as soldiers. In the end, Dazai arrives at the location, only to find that Oda and Gide have shot each other. In his final moments, Oda advises Dazai to choose to be on the good side and help others.

After the incident, Yokohama returns to its former regular conditions. En route to a mission, Ango earnestly looks over some of his personal photos. Somewhere in Yokohama, Akutagawa finishes off three residual Mimic soldiers, pleading to have him fight someone stronger to have "that" person acknowledge him. At a cemetery on a hill, Dazai leaves the photograph of Oda, Ango, and himself together at the bar on Oda's epitaph. In his office, a mafioso notifies Mori that Dazai has been uncontactable for two weeks and proposes that they choose a new executive to replace him, but Mori orders to keep Dazai's spot empty.
 * Epilogue

Sometime later at a pub, Taneda is approached by Dazai, who asks him if he knows someplace where he can work and help people. Initially suggesting that he work for the Special Division (an offer that Dazai declines), Taneda later recommends him to a certain gifted armed organization, which ultimately piques Dazai's interest.

Involved Parties

 * Port Mafia
 * Mimic
 * Special Division for Unusual Powers

Trivia

 * According to Asagiri, the origin of the novel's title is modelled after Pablo Picasso's Blue Period, which comprised rather somber works believed to be caused by Picasso sinking to desolation. In a similar fashion, Dark Era portrays Dazai going through a dangerous period in his life, which Asagiri compares to that of a "dark spring" rather than a "green spring" symbolizing a time of blooming.
 * The story became an collaboration event of Bungo Stray Dogs with Love Heaven, whose developer is the same as the one who created Bungo Stray Dogs: Mayoi Inu Kaikitan. It also became a collaboration event for Eighteen: Dream World.