Bungo Stray Dogs: Osamu Dazai's Entrance Exam

Bungo Stray Dogs: Osamu Dazai's Entrance Exam (文豪ストレイドッグス 太宰治の入社試験,) is the first light novel in the Bungo Stray Dogs series. It details Osamu Dazai joining the Armed Detective Agency through Doppo Kunikida's perspective.

The light novel consists of eight chapters in total, which were adapted into the Bungo Stray Dogs anime, filling in Episode 6 and Episode 7 of the series.

Description
Doppo Kunikida is an idealist and a straitlaced detective at the Armed Detective Agency, an organization that takes on dangerous jobs even the police won't handle. Everything in his life is going just as he's planned...until one day, he's paired up with the agency's newest hire: a suspicious, eccentric, suicide-obsessed man named Osamu Dazai. Their first case together turns out to be far more complicated than Kunikida anticipated — and it looks like the detective agency's sworn enemy, the Port Mafia, is somehow involved, too!

Set two years before the events of the manga series, this is the tale of how two seemingly incompatible personalities end up forming the partnership that has made them one of Yokohama's top detective duos.

Summary
Doppo Kunikida contemplates on what ideals are, ranging from taking the forms of stories, ideologies, or even the source of all meaning. For him, "ideals" is a word written on the cover of his notebook, which he believes holds his entire future and his ideals. Upon introducing himself, his daily life and tasks as a member of the Armed Detective Agency are shown in a glimpse, including catching criminals who disturb the peace and order of Yokohama.
 * Prologue

Kunikida reminisces the time when he is partnered with Osamu Dazai upon the referral of Special Division for Unusual Powers director, Santōka Taneda. Customary for new hires, Agency president Yukichi Fukuzawa entrusts Kunikida with Dazai's entrance exam. He also instructs Kunikida to kill Dazai if he discerns that he is related to a plot that might harm the Agency, more so because of his suspiciously clean records and unusual nullification ability.
 * Chapter 1

Later, Kunikida receives an anonymous e-mail requesting the Agency to investigate an ostensibly haunted building. With the help of Rokuzō Taguchi, a 14-year-old informant hacker, they trace the client's whereabouts and are driven by an acquainted taxi driver to an abandoned hospital. There they find a shackled woman, Nobuko Sasaki, drowning in a cistern and four people trapped in a cage. Though Sasaki is rescued, Kunikida and Dazai are unable to save the four after a poison gas is released to the cage.

The four victims are apparently Yokohama visitors who have disappeared upon their arrival, an ongoing case being investigated by the Agency. News articles and images also surface depicting the Agency's failure to save the four victims that caused their deaths. Kunikida surmises that someone has candidly photographed the event and released the photos to the public, which Dazai thinks is the culprit's objective.
 * Chapter 2

Eventually, Kunikida realizes that the culprit to the visitors' disappearances is their taxi driver. The driver soon confesses to kidnapping the visitors and asks for a witness protection deal for fear of being targeted by the Port Mafia after dropping an organ trade market on them. Mafiosi then attack the taxi during their conversation, compelling Kunikida to fight Ryunosuke Akutagawa. Their clash is later thwarted, and Dazai is able to protect the driver during the shootout, who is handed to the police.

After the driver's arrest, Kunikida receives a new request from the same client, signed as the Azure Messenger. This time, the Agency is asked to deactivate a large-scale bomb.

At night, Dazai waits inside a car in a deserted parking lot. As he muses on finishing their tedious task, Dazai types on his laptop and wonders whether the Agency, and by extension Kunikida, would be able to see through the enemy's trap and protect Yokohama.
 * Interlude 1

Sasaki later sees a possible relation between the Azure Messenger and the Azure Banner Terrorist Incident, whose culprit known as the Azure King died in a blast that claimed lives, including Rokuzō's father. Later, Kunikida and Dazai are told at the American embassy about a foreign bomber, Zadkiel Alamta, whom they suspect to be the Azure Messenger.
 * Chapter 3

Ranpo Edogawa, the Agency's senior detective, soon aids them with his ability, Super Deduction, and infers that the bomb is located at a fishing tackle shop. Dazai is also impressed with Ranpo's mere deduction, revealing to Kunikida that Super Deduction is not an ability after trying to nullify (and failing to cancel out) said "ability". They later arrive at the area to locate the bomb, only to find Alamta's corpse nearby. Not long after, they are notified that the taxi driver has also died.

Along the way, Rokuzō tells Kunikida that the e-mails were sent from Dazai's computer. Initially in disbelief, Kunikida realizes Dazai may be the enemy, who has always been a step ahead in their operation as if they are constantly monitored. Per Fukuzawa's earlier instruction vis-à-vis Dazai's possible evil nature and due to recent revelations that appear to claim Dazai as the Azure Messenger, Kunikida shoots Dazai at an empty warehouse. Afterwards, however, Agency doctor Akiko Yosano tells Kunikida that the Azure Messenger has sent another request to stop a passenger aircraft from crashing.

Kunikida's confrontation with Dazai turns out to be a ruse, after figuring out earlier that Dazai was being framed as the mastermind with incriminating items planted on him, including a blue banner and a listening device in Dazai's pocket, which apparently signaled the true culprit to launch the third threat after hearing Dazai get "shot". They soon track the transmitter signal paralyzing the aircraft's systems in a former defense force facility.

Upon arriving, Kunikida faces a number ability user who breaks the transmitter signal's cancellation key, while Dazai struggles fighting a gigantic man. Overwhelmed by their opponents, they soon switch places. Kunikida beats the large man with his physical prowess, and Dazai nullifies his opponent's ability. Kunikida reproduces the cancellation key with his ability, The Matchless Poet, and prevents the aircraft from crashing.

After a few days, Kunikida reports to Fukuzawa about Dazai's character and allows him to pass his entrance exam. Later, Kunikida chances upon Sasaki at a cemetery where she tells him about her deceased lover. Dazai then calls Kunikida to the abandoned hospital and tells him that he has sent an e-mail to the true Azure Messenger to settle matters at the place.
 * Chapter 4

Rokuzō arrives, making Kunikida think that he is the Azure Messenger. However, Rokuzō is suddenly shot by Sasaki, who turns out to be the actual Azure Messenger. Sasaki has been seeking to avenge her deceased lover, the Azure King, because the Agency (specifically Kunikida) had discovered the Azure King's whereabouts during the terrorist incident that led to his death.

With Dazai's gun kicked earlier near his direction, the injured Rokuzō shoots Sasaki as revenge for his father's death, after which they both succumb to their wounds. With Kunikida questioning Dazai's methods, the latter advises him to stop chasing an ideal world, claiming that Kunikida will merely harbor the Azure King's rage one day if he does not stop.

In the aftermath of the incidents, Akutagawa finds and kills the number ability user for using the taxi driver and tricking the Port Mafia during the organ trade deal. He is also approached by a Caucasian man whom Kunikida and Dazai met at the embassy, who reveals himself to be a secret agent also working for the Guild. In the end, Akutagawa pursues his quest in finding ex-mafia executive and his former mentor, Dazai.
 * Interlude 2

Two years later, Jun'ichirō Tanizaki tries to find Dazai with a transmitter on him and locates him by a river. Kunikida then sets off to fetch his partner to continue their investigation of capturing a certain tiger who has recently wreaked havoc in Yokohama.
 * Epilogue

Involved Parties

 * Armed Detective Agency
 * Port Mafia