Episode 43

Sunday Tragedy (悲劇なる日曜日,) is the 43rd episode of Bungo Stray Dogs anime series and the sixth episode of the fourth season. It aired on February 8, 2023.

Summary
One month after the Cannibalism incident, Fukuzawa and the Armed Detective Agency are awarded by the Ministry of Justice for ensuring the safety and protecting Yokohama during the fall of Moby Dick. Meanwhile, Kunikida trains Atsushi in physical combat, mentoring him that he should not always rely on his tiger prowess but focus more on his own individual strength. Later, they convene with the Agency to discuss a new case regarding a murder society who has brutally killed four key figures within the past week.

Ranpo deduces the culprit to be the Decay of the Angel, the term of which Fukuzawa explains also refers to the five signs exhibited by before their decline. As the "five signs" coincide with the four grisly murders, Fukuzawa tasks the Agency to prevent the fifth murder from occurring. However, on account of Mushitarō's previous warning, Ranpo turns down the job and storms out. Kunikida tries to stop him, only for Fukuzawa to let Ranpo go as they conduct a dual investigation: while the Agency tackles the case, Ranpo shall investigate the Agency's impending downfall.

Unable to contact Dazai, Ango warns Atsushi that the Decay of the Angel might be a front of a particular government party. Atsushi soon encounters Justice Vice Minister Tonan and grows dubious of him before taking his leave. Tonan then mutters to himself that the Agency's doom shall arrive in no time. At a racing stadium, Dazai is arrested by a blind man for his past crimes as a former Mafia executive. The man turns out to be part of the Hunting Dogs, tasked by Tonan and his accomplices in their quest to expose and crush the Agency for their crimes.

Tonan is later given by his secretary documents listing the orders given to Fukuzawa in assassinating leading war hawks in the past, including Tonan's father. He asks his secretary to set a meeting with the intel provider, at which the secretary, revealing himself as Nikolai, fires at Tonan. The Hunting Dog also explains that evidence has re-emerged recently; this turns out to be caused by Mushitarō, bound and beaten, undoing his ability, realizing that such is his primary use in the entire operation for which he has been lured in.

Holding Tonan and his party hostage, Nikolai contacts the Agency and lists the circumstances: that the hostages are seated in chainsaw-rigged chairs, that the chainsaws will activate if anyone outside the Agency intervenes, and that the chainsaws will activate at exactly six o'clock. With 30 minutes remaining, Kunikida informs Ranpo about the details, while Ranpo himself locates Special Division director Taneda critically wounded and informs him what the Decay of the Angel is after.

Atsushi is sent in ahead of the others to disable the timer at the hostage taking site. Passing in the underground escape route, he is ambushed by Nikolai and engages him in a skirmish, where Atsushi figures out the clown's matter teleportation ability and gets immobilized in the end. Taneda tells Ranpo that he has been stabbed by a Decay of the Angel member who can exchange information with them and the target, thereby learning that the five-man organization—which Ranpo surmises might possibly be V—has stolen a page from the Book and urges Ranpo to abandon the case, as the Decay of the Angel aims to use the Agency as a catalyst for doom.

Nikolai returns to the hostage taking site, where the Agency arrives and tasks Kenji to stop the incoming military police from intervening. As Nikolai releases Tonan from his restraints, Kunikida and the others plan their attack; however, Nikolai has the chainsaws activate at once and has the terrorists remove their hoods. The Agency suddenly find themselves to be the hooded terrorists and Nikolai bound in a chainsaw chair. The MP discovers that Tonan's meeting is about exposing the Agency's crimes, while Nikolai's chainsaw activates and bisects his body like the others. Ranpo calls Kunikida to escape immediately, only for Tonan to contact the MP and name the Agency as the Decay of the Angel.