Cannibalism Arc

The Cannibalism Arc (い編,) is the fourth story arc of Bungo Stray Dogs. It introduces a new group of antagonists, the Rats in the House of the Dead.

Synopsis
A new criminal organization called the Rats in the House of the Dead makes its existence known to the Agency. Little is known about it and its alleged leader, Fyodor Dostoevsky, but a downward spiral begins when Yukichi Fukuzawa is attacked and left gravely ill. Both him and the Port Mafia's leader, Ōgai Mori, have been infected with a virus named Cannibalism. After forty-eight hours, the virus will destroy the hosts' internal organs, unless one of them dies before the virus outbreak, thus nullifying the other's illness. The Agency and the Port Mafia start a blood feud to save their respective leaders before it is too late.

Attack of the Masked Assassin
Fukuzawa is seen strolling during the night when he sees bloodstains on the pathway. He immediately follows the trails and is suddenly attacked by a masked assassin, but successfully counters the attack. Out of nowhere he is then shot by poison, which causes him to lose consciousness.

Due to the attack and the possible damage it could cause the Port Mafia, the Mafia takes on the action to find the assassin's hideout, but is a step too late.

Mori is seen together with Elise doing shopping, when the car they entered explodes. Mori is barely saved by Elise. Mori is contacted by Akutagawa, updating that the masked assassin has been caught in the net. Akutagawa takes on the masked assassin and learns his true identity, the Guild's Nathaniel Hawthorne, who apparently doesn't have memories of his own.

Meanwhile, Dazai investigates the pathway Fukuzawa was attacked on, and deduces who the killer is.

After the car explosion, Mori and Elise are approached by a police man asking their situation. Mori reassures the policeman and tells them they are fine. The police man suddenly stabs Mori, revealing himself as Fyodor Dostoevsky. Elise tries to catch up to Fyodor, but loses him in the crowd.

Dazai confronts Fyodor about the poison he used with Fukuzawa, and relays that he knows what he's after - to secure the book to wipe Yokohama of ability users. He reveals the poison injected is imbued with a cannibalism ability - in order to save the one, the other one has to die. During their conversation, Dazai is shot by a sniper eventually left by Fyodor.

Attack of the Port Mafia to the Agency
The cannibalism virus slowly affects Fukuzwa and Mori's lives. Learning that the way to disable the virus is to have the other one dead, the Mafia takes on the first action to attack the Armed Detective Agency. Meanwhile, the Agency has decided to guard Fukuzawa's room and defend him from the Port Mafia forces.

This reveals to be a decoy by Jun'ichirō Tanizaki's Light Snow. He reveals that the other agency members have taken Fukuzawa out and relays Ranpo's message to capture the ability user who created the virus. Tanizaki is then held hostage by the Port Mafia.

During the agency's escape, Ranpo tells the agency that having a frontal assault on the mafia is guaranteed to lead to deaths, hence they will be changing the rules - track down the culprit and have Dazai touch him using his ability (which nullifies other Abilities).

Pursuit of the Virus Ability User
Kunikida and Atsushi set off to the hideout of the virus ability user named Alexander Pushkin. During their pursuit of Pushkin, they are intercepted by a group of armed children who are giving the virus ability user, their older brother, time to escape. Kunikida and Atsushi face the armed children, eventually hurting some of them in the process. Eventually, a child with an attached bomb sets off the bomb upon remembering Fyodor's words that the man with the notebook(Kunikida) is a dangerous man.

Atsushi soon catches up to the virus ability user and restrains him. The man turns out to not be Alexander Pushkin, whom they are pursuing. At the underground tunnel, Kunikida survives the explosion and sees all the children dead as a result of the blown up rocks. Yosano and Ranpo arrive to Atsushi's aid. The man gives the agency a police file about the virus ability user which also turns out to be a fake and relays Fyodor's message about "no changing the rules".

Armed Detective Agency and Port Mafia Stand-off
At the Port Mafia base, Tanizaki is seen being held hostage. Tanizaki is threatened to leak the agency's interals otherwise Gin, an assassin, will "take care of" his younger sister. Tanizaki provokes Michizō Tachihara, who is pointing a gun to him. Tanizaki manages to remove the ties around his hands thanks to Kunikida's ability. Eventually, Tanizaki manages to escape from Black Lizard's watch and proceeds in planning to murder Mori.

However, he is attacked by Kōyō Ozaki. Tanizaki is then saved by Kyōka's arrival. Tanizaki and Kyōka both escape from the building. Fukuzawa is revealed to be confined in Anne's chamber.

The agency regroups, deciding whether to fight the mafia or not. He tells that once the mafia knows Fukuzawa's whereabouts, they will resort to terrorism including capturing the agency's family, friends, eventually threatening them if the agency won't bring Fukuzawa out. Due to this, some of the agency members including Ranpo, Tanizaki, Yosano, Kyōka, and Kenji decide to fight the mafia. Meanwhile, Atsushi still decides to track down the culprit with the help of Katai Tayama.

Seventeen hours left until the virus outbreak, Kenji, Tanizaki, and Yosano infiltrate the Port Mafia building. Upon infiltration, they are attacked by the Port Mafia guards. The infiltration soon fails when Motojirō Kajii comes out bringing lemon bombs for explosions, making the agency members have to pull back. Ranpo, on the other hand, faces Chūya Nakahara and traps both of them into a novel. Kyōka threatens Ichiyō Higuchi to give the code to the safe room where Mori is sleeping. The interrogation is interrupted by Akutagawa's presence. Akutagawa and Kyōka face and attack each other. Their fight is halted due to Motojirō's bombs.

At Katai's apartment, Astushi and Kunikida are unable to find Katai in the room. The two proceed to check the footage of the room's hidden camera, which reveals Katai being shot by Fyodor.

At Anne's chamber, Fukuzawa hears about what's happening outside , and decides to leave the chamber to meet with someone.

Battle of Fukuzawa and Mori
Fourteen hours left until the virus outbreak, after fleeing the Port Mafia building, the agency members have learned that Fukuzawa is gone. The mafia also learns that Mori has left the building in his own volition.

Fukuzawa and Mori both arrive at a western-style building and decide to face each other in order to halt the "cannibal" with one of their deaths.

Twelve hours left until the virus outbreak, the agency investigates as to where Fukuzawa must have gone. Dazai is seen recovering at the hospital due to the shot he received when he met Fyodor.

Fukuzawa and Mori then soon attack each other, eventually resulting in Fukuzawa's defeat. The battle is interrupted by Sōseki Natsume's presence, who tells the two leaders that Katai has uncovered the enemy's hideout, and orders the two to act before the foes are able to disappear again.

Pursuit of the Rats
Dazai has teamed up Akutagawa and Atsushi to infiltrate the enemy's hideout. Upon arriving, Akutagawa successfully gets past over the guards and infiltrates the hideout using Rashomon. Atsushi also catches up to Akutagawa at the hideout. The two soon set off to find the virus ability user, and learn about a bombproof metal door that could be the enemy's HQ.

Meanwhile, Fyodor is seen communicating with a mafioso regarding the update on both the agency and mafia's leaders.

Akutagawa and Atsushi arrive at the metal door. However the door will be hard to open due to network speed, hence Akutagawa telling Katai to prioritize locating the enemy. After some time, Katai contacts them and tells them that he have found the virus ability user's location which happens to be two meters behind them. Akutagawa is affected by the virus after being shot. Pushkin then leaves them and escapes.

Pushkin is seen talking to Ivan Goncharov while escaping to carry out his next order, which is to make it out alone. Pushkin shoots Akutagawa and Atsushi while escaping, eventually destroying the mine cart they were in. During their pursuit, Pushkin gets away, but Atsushi manages to catch up to him using his ability. However, they were interrupted by Goncharov's appearance.

Meanwhile, Dazai is commanding Tanizaki and Kenji while patrolling the enemy's hideout in order to catch Fyodor. Back at the old mine, Akutagawa and Atsushi face Goncharov. The agency has failed to locate Fyodor at the enemy's hideout.

With the virus slowly deteroriating Akutagawa's life, he decides to let Atsushi use Rashomon together with Beast Beneath the Moonlight. Atsushi eventually overpowers and defeats Goncharov using the power of Beast Beneath the Moonlight Rashomon: Black Tiger's Supreme Claw. Pushkin manages to escape the mine, only to find the agency and mafia waiting for him outside. The virus eventually vanishes after Pushkin is confronted.

After the battle, Goncharov reveals that Fyodor was never at the hideout in the first place, and reveals that their communication was through music by picking up the radio signals and communicating orders from a radio show. Fyodor is seen at a cafe somewhere. Upon leaving, he sees Dazai waiting outside together with Francis Scott Key Fitzgerald. He reveals that he found Fyodor using the Eyes of God. Fyodor is then arrested by the Special Division for Unusual Powers.

Aftermath
At the aftermath, the agency is seen at the S.S. Zelda having a celebration after the event. On the outside, Dazai asks Atsushi how is it like working with Akutagawa, to which the latter describes it as awful. Atsushi then reveals an agreement he made with Akutagawa, this agreement being that Akutagawa can kill Astushi as long as he doesn't kill anyone for Six months. Akutagawa agrees to the agreement.

Appearances
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Impact

 * Fukuzawa and Mori's shared past is explained.
 * Sōseki Natsume appears for the first time in his human form. Until now, he has been only seen in his cat form as Kirako Haruno's cat, Mii-chan.
 * Four members of the Rats in the House of the Dead have been identified: the leader Fyodor Dostoevsky, the virus ability user Alexander Pushkin, the former Guild member Nathaniel Hawthorne,   and Ivan Goncharov.
 * Fyodor is arrested.