Chapter 40

Walking Alone (独り歩む,) is the 40th chapter of the Bungo Stray Dogs manga.

Summary
Osamu Dazai comments on how packed Doppo Kunikida's schedule is, pointing out that the ADA has received multiple time-sensitive cases and requests. Undeterred, Kunikida intends to go about his scheduled day. Akiko Yosano asks him to go shopping, which he swiftly denies. Meanwhile, Jun'ichirō Tanizaki mentions a bomber giving rigged suitcases to civilians, and Ranpo Edogawa complains about a lack of snacks. Both are disregarded in Kunikida's desire to keep up with his schedule. Just before he leaves, he demands Dazai not interfere with his schedule, which Dazai assures he won't - not that Kunikida believes him.

At the train station, Kunikida's schedule is inevitably interrupted by Dazai. He tells Kunikida that Carlyle, the man who made Kunikida's notebook, is visiting, much to Kunikida's excitement. He readies himself to meet Carlyle, but the train arrives, much to his dismay.

Just before boarding the train, Kunikida notices a man donned in black handing a young girl a suitcase, immediately recalling the bomb case Tanizaki mentioned. He rushes to take and throw the suitcase over the railing of the station, and it explodes instantly after. He calls to make sure authorities get on the scene, and goes to comfort the seemingly despondent girl. He's shocked by her anger over the black-dressed man trying to deceive her, more so when she forcibly drags him along to confront the culprit himself.

Kunikida attempts to dissuade her, but the girl insists she is a "Warrior of Justice", claiming to practice martial arts every day and refusing to sit back in the face of crime and injustice. Kunikida remains firm, but Aya rips her clothes and threatens to frame Kunikida of sexual harassment. Forced to give in to her demands, Kunikida relents. The girl introduces herself as Aya, and leads the way to the culprit.

Back at the Agency, Kenji Miyazawa asks Tanizaki whose second-in-command of the Agency. Tanizaki wonders aloud if it's Ranpo, given his "ability" and experience, but Ranpo points out he has no interest in such a position. Tanizaki assumes Dazai then, but Dazai is too occupied thinking of ways to annoy Kunikida to confirm or deny Tanizaki's assumption.

In the tunnel, Kunikida and Aya make their way to the culprit. When questioned why he puts so much weight into his schedule and ideals, Kunikida explains that a world where people die isn't ideal to him, so he strives to save lives instead.

He notices bombs laid along the train track, meaning that once a train came through, the bombs would instantly detonate. He ponders the familiarity of the bomb's type and modus operandi, but quickly shifts gears to focus on finding a remote device to disable all the bomb traps. Yet, when he turns to inform Aya, she is missing. His search ends in finding a terrified Aya with a bomb strapped to her neck. The culprit appears behind him, ordering him to discard his gun lest the bomb on Aya detonates. Kunikida obliges, and is knocked out and tied to a pillar by the culprit.

When Kunikida wakes up, the culprit reveals he knows everything about Lone Poet. Combined with his knowledge and MO, Kunikida identifies the young man as Shōsaku Katsura.

Two years ago, Shosaku attempted to detonate a bomb at a school, however, Kunikida (still part-timing as a teacher at the time), caught and arrested him. Kunikida assumes the arrest is why Shosaku leaked his own bombings to the Agency, for revenge against Kunikida. However, Shosaku corrects him: the goal was not revenge, but to "erase" Kunikida's ideals from his head when told them during the arrest. Shosaku proceeds to beat and berate Kunikida for his ideals. Composed and bloodied, Kunikida tells him to look at page 86 of his ideals journal. Shosaku opens a trap, allowing the book to manifest a stun grenade, which detonates, alarming citizens above the tunnel and allowing Kunikida to pin Shosaku down.

Kunikida discovers the signal to disarm the train explosives and the signal detonating Aya's bomb are the same, forcing him to choose the train passengers' or Aya's life over the other. Shosaku is smug in thinking he has Kunikida cornered, but Kunikida and Aya both agree to save the passengers. The bomb on Aya goes off, seemingly killing both of them.

Yet after the bomb smoke dissipates, the duo are practically unscathed and, more importantly, alive. Shosaku is shocked.

Behind Kunikida, Akiko appears. She explains that when the stun grenade went off, she hurried to the scene, making it just in time to save Kunikida and Aya with Thou Shalt Not Die. Her presence at the station marked down by Kunikida when she informed him she'd be off shopping. Along with alerting Akiko, the stun grenade succeeded in summoning riot squad to the scene to arrest Shosaku.

In the aftermath, Aya comments on how someone with naive ideals like Kunikida's doesn't have a girlfriend. Kunikida immediately shuts her down, pointing out she doesn't meet 31 of his 58 ideals for a girlfriend.

At the Agency, Dazai finally answers who will be Yukichi Fukuzawa's successor: a person who can lead others, handle affairs with composure, and is an unwavering person aware of their own shortcomings - Kunikida.

Trivia

 * In the OVA adaptation of Chapter 40, both Atsushi Nakajima and Chūya Nakahara make small appearances, despite having no relevance to the plot.