Echo is the 51st chapter of the Bungou Stray Dogs manga.
Dazai, Atsushi and Akutagawa are seen in a moving truck while Dazai jokes around with them. He tells them that they should go after the virus ability user and then Dostoyevsky. At the suspected place of the Rats(a coal mine), many guards armed stand watch. As Atsushi and Akutagawa sneakily head in, the Agency stays alert to make sure none of the guards suspect a thing. In the mine, Akutagawa is determined not to disappoint Dazai and threatens to kill Atsushi so he can do the mission alone. They get into an argument but Atsushi goes a little too far resulting in Akutagawa going silent. Suddenly, the two spot two guards and Akutagawa activates Rashomon. Akutagawa corners the two guards and demands that they lead him to their leader. The two agree. Akutagawa and Atsushi are led to a door that is locked. With Katai's help, they try to unlock it but the security is too high. Suddenly, Katai tells them that he has discovered the virus users location; two meters behind them. The virus user named Pushkin shoots Akutagawa. Akutagawa falls down and is infected with the virus.