: The episode features a young Sakunosuke Oda as a cold, efficient teenaged assassin, paralleling the nihilistic views later seen in Dazai. Key Episode Details Information Title "The Lone Swordsman and the Famous Detective" Release Date January 4, 2023 Source Material The Untold Origins of the Detective Agency (Light Novel) Opening Theme "True Story" by SCREEN mode Ending Theme "Shirushi" by Luck Life Analysis & Visual Style
: The use of monochrome visuals throughout the episode serves to highlight the "colorless" world Ranpo perceives before meeting Fukuzawa.
The fourth season of premiered on January 4, 2023, produced by Studio Bones . The first episode deviates from the present-day timeline to adapt the light novel The Untold Origins of the Detective Agency . Plot Summary
: Fukuzawa is stunned by Ranpo's deductive power. Despite his desire to work alone, Fukuzawa takes the boy under his wing, promising to help him find work if he assists with a death threat case involving a theater performance.
: A 32-year-old Yukichi Fukuzawa , working as a stoic freelance bodyguard to distance himself from his past as a government assassin, encounters a 14-year-old Ranpo Edogawa at a crime scene.
: Ranpo, an orphan struggling to hold a job because he views the world as "too simple," immediately solves a murder mystery that had the police stumped.
Set roughly 12 years before the main series, the episode is presented in a cinematic grayscale "noir" style.