Mushitarō Oguri/Synopsis

Cannibalism Aftermath Arc
Ranpo is about to examine a suicide case, which is in fact not a suicide at all. In truth, it is a murder case in which he suspects as the way "the Cleaner" would camouflage himself. Among the crowd of witnesses, Mushitaro activates his ability, erasing all the evidence of the crime. As Ranpo uses his deduction on the victim to locate the murderer's location, he suddenly looks up at Poe with a worrisome look, stating that he does not know anything given the lack of evidence left by the murderer. Mushitaro then proclaims himself as the "detective killer", saying that there is no way Ranpo can prove Doppo Kunikida's innocence nor why Fyodor let himself get caught by the government. He then compares the action of getting away with murder to taking candy from a baby, just like what he has done several days ago.

As he succumbs in his own self-glorification, Ranpo tugs his shoulder from behind, asking Mushitaro where the taxi stand is. Mushitaro, who is currently waiting for the extractor's vehicle, looks evidently troubled as Ranpo may suspect anything if he were to see the extractor. In order for the plan to go smoothly, Mushitaro assigns Ranpo to a train station five minutes away from them or to a bus stop, both of which Ranpo refuses. He instead requests Mushitaro to let him ride on his back. In that moment, the extractor arrives, and Mushitaro bids Ranpo a farewell as he enters the car bound to the Yokohama smuggling harbor to escape the country.

Mushitaro, being too preoccupied with his mind, is oblivious to the fact that Ranpo has entered the car sitting beside him. In exchange for letting him ride in the car, Ranpo promises to offer Mushitaro some job if he were to lose it. He then tries to avert Ranpo's attention by asking about him as the car heads to the bus station to drop Ranpo off.

The detective tells Mushitaro about Kunikida's false charges and the "falling murder" he witnessed earlier. Mushitaro, pretending not to know the murder case, absent-mindedly states that he is not interested in detectives and murder. Ranpo replies that it is only natural that the case is so difficult because the culprit has a reality-altering type of ability, causing Mushitaro to get taken aback at how far Ranpo has gotten. Ranpo voices out how he got stumped with the case, since his reasoning cannot overcome a reality-altering ability; however, Ranpo states that he has managed to solve it. He connects the falling murder case with the recent murder case of the author known as Kindaichi, deducing that the Cleaner and the author's murderer are both the same person. He reveals the hidden manuscript that he found in a photocopying shop and, as its proof, names Mushitaro as the culprit in both cases.

The extractor points his gun towards Ranpo, but Mushitaro asks him to put his gun away so as not to give the detective any excuses. Ranpo then reveals how he has planned the situation and how Poe has been listening to their conversation since the start. As Minoura arrests Mushitaro and the extractor, the latter invokes his diplomat rights, allowing the two to get away from the police. Ranpo then calls Mushitaro on his phone, telling him how, though he acknowledges his limit as a detective compared to an ability user, he shall do anything in his power to help his comrades given their trust in him. Mushitaro reads the foreign text on his phone and gets transported to an inn, with Yokomizo strangling him. He soon realizes it is one of Poe's novels, and Ranpo visits him in the setting to settle the matter with him.

Mushitaro commends Ranpo's insistence in proving his guilt, but he reminds the detective how he can easily get out of the setting once he tells the truth of the case. Ranpo assures him, however, that he will surrender after the confrontation. Recalling his moments with Yokomizo before his death, Mushitaro confesses that he has indeed killed the author, but Ranpo believes that he did not, thinking how it is too scripted or formulaic. Instead, he thinks that the author killed himself. Nonetheless, Ranpo recognizes the infamous story's effect among the public, almost becoming the "ultimate mystery" that no one can solve. Mushitaro ominously commends Ranpo for correctly deducing him as the murderer who killed his friend out of hatred. However, Ranpo deduces that Mushitaro photocopied the final manuscript with an ink blot because it has been wet with his tears and so must avoid his tears getting analyzed; he then hid it at the last minute knowing that he must discard it in his possession.

Thus, Ranpo deduces that the murder's motive is to fulfill his friend's final wish, which is to complete the ultimate mystery that transcends reality. In case Mushitaro still does not wish to surrender, Ranpo threatens to have his hypothesis publicized, which might stir gossips among the public and devalue Yokomizo's legacy. Realizing how he must keep his friend's final wish, Mushitaro surrenders himself to the authorities and revokes his ability on Kunikida's accusations. Ranpo and Poe find out that the victim of the falling murder is actually a dummy, making it possible that Mushitaro might not have committed a crime in the first place. Ranpo approaches Mushitaro in the police car and offers him a calling card to a Special Division for Unusual Powers undercover agent, who might have his ability utilized for their services.

Along the way, the police vehicle leaves and encounters a ruckus nearby. The driver asks a police officer about the commotion, to which the latter shoots him at point-blank range.

Hunting Dogs Arc
Mushitaro witnesses the crime from the back seat and recognizes the culprit to be Nikolai Gogol, a member of the Decay of Angels and one of Fyodor's comrades. As Gogol introduces the Decay of Angels and their terrorism act, Mushitaro immediately grabs the police car radio and advises Ranpo not to take the next case to be given the Agency, before getting cut off with gunshots at the end of the line. He is later shown to be battered up and his ability revoked, causing various evidence to resurface, including Osamu Dazai's criminal records during his time as a Port Mafia executive.

Sky Casino Arc
In the wake of the hunt for the Agency, Mushitaro is visited in his cell by Atsushi Nakajima and Kyōka Izumi, who seek information from him about the Decay of Angels to help prove the Agency's innocence. Mushitaro refuses to leave the government bank where they are, so Kyōka utters the word "manuscript", which is a threat by Ranpo spilling the truth behind his friend's case. Hence, Mushitaro agrees to come with them, albeit plotting to have them caught by the authorities. He puts on various acts to have them cornered, but Kyōka scares him off with her threats every time, causing him to fail.

However, as soon as he spots Ango Sakaguchi and the Special Division troops outside, he frantically decides that they must escape at once and avoid capture from Ango, whom he recognizes as the head of the criminal group known as the Seventh Agency. They escape from the surveillance cameras using his ability, but they soon find themselves about to be cornered by the troops. Amidst their panic, Yokomizo appears to him, causing Mushitaro to get inspired in escaping their pursuers.

They employ a classic locked-room trick to hide from the Special Division troops, causing them to exit the bank successfully. As they plot to steal a runaway car, Atsushi and Kyōka are hit with tranquilizing darts by Ango, who reveals how he has pinpointed their escape route using his ability. As the Special Division begin to arrive, Ango pushes the group down the sewer for them to hide and misleads his troops to a different direction.

The four leave the area by Ango's car, where he reveals that he is Dazai's middle-man while he is imprisoned. Mushitaro voices out his distrust for a crime boss like Ango, to which the latter admits that he is actually not part of the Seventh Agency and is a mere lie made up by Fyodor. They head to Lucy Maud Montgomery's dimension, who previously marched into the Special Division headquarters defending the Agency's innocence.

Mushitaro confronts Ango and asks him whether he has ever employed the Seventh Agency's services, to which Ango responds that he has once asked them to erase Dazai's crimes as atonement for their friend who has passed away, which Mushitaro somehow understands. Ango, Atsushi, and Kyōka then ask for Mushitaro's information on the Decay of Angels. Initially reluctant, he warns them that any news they hear from him shall become the worst possible news they ever learn.

Ango asks what the organization really is, to which Mushitaro explains that the Decay of Angels is a five-man murder association headed by an "overseer". Though he does not know their end goal, he tells them of the previous steps and the step before their end goal, which is to eliminate the country using the back page of the Book within ten days. Afterwards, Mushitaro is escorted out of the chamber by Ango.