Gaiden Chapter 5.1

Inside Passenger Train / Morning / Cloudy ① (旅客列車内／午前／曇天　①,) is the first part of the 5th chapter of the Bungo Stray Dogs Gaiden manga.

Summary
Aboard the train prepared for them, Kubo interviews Ayatsuji about his work, asking how long the detective has been doing his job, how many cases he has solved, and how many he has killed. Ayatsuji briefly answers all: 20 years in the job, 50,000 cases solved, and two billion victims killed.

Kubo bitterly tells Ayatsuji not to look down on him, especially since he took the train to return to his hideout unlike Ayatsuji who was threatened to board it. The latter merely shrugs it off as something that would be bragged about by one who uses knowledge from the Well, taking Kubo aback.

Ayatsuji expounds that the infamous Well that supposedly grants humans evil is only an urban legend but has a cunning "screening system", particularly a book number shown at the end of the Well. He notes it to be the first edition of The Selfish Gene, which was published in 1976 and is highly difficult and hefty to acquire. He adds that additional information is sent to whoever acquires it, which, in their case, is how the first follower of the Well came to know Kyōgoku. Moreover, the one who can acquire all qualifications of evil—who can dirty themself in mud, research about the Well with utmost dedication, have knowledge in cracking the code, and can purchase the expensive book—shall be bestowed with the knowledge of the perfect crime, which Ayatsuji describes to be the true demon who resides in the Well.

Kubo is impressed with how much Ayatsuji has uncovered, though the detective claims that he has merely solved everything from the hints throughout the incident. He then receives a call from his earpiece and begrudgingly takes it, which he thinks must be from Kyōgoku.

Characters in Order of Appearance

 * Mizuki Tsujimura (cover)
 * Yukito Ayatsuji
 * Kubo
 * Natsuhiko Kyōgoku (flashback)

Trivia

 * ' is a real-life book on evolution by in 1976. Building upon the principal theory in the 1966 book ' by, Dawkins uses the term "selfish gene" in expressing a gene-centred view of evolution.