Tonan (斗南, Tonan?) is the Vice Minister of Justice.
Tonan is a middle-aged man with light, straight hair and bangs partially swept to his forehead that covers his right eye. He wears a pair of glasses and often wears a suit comprising a light shirt, necktie, jacket, and a pair of trousers.
Tonan harbors a deep hatred towards Yukichi Fukuzawa for assassinating his father and other war hawks during the end of the Great War. By extension, he detests the Armed Detective Agency and is willing to resort to any means in exposing their crime-related feats. Clinging to a sense of vengeance for his father, he has been gathering various evidence within his jurisdiction to bring the Agency's past and concurrent crimes to light.
Tonan's father was assassinated during the Great War, among countless other war hawks, by Yukichi Fukuzawa. From then on, he vowed to avenge his father by gathering evidence that prove Fukuzawa's and the Armed Detective Agency's crimes, such as protecting a killer of 35 people, colluding with the mafia, and the doctor's suspected murders of her patients during operations while she was a military physician.
At some point, six months until the events of Cannibalism, Tonan organized a secret group of government officials with the agenda of bringing charges of guilt against the Agency, unbeknownst to them that they had been aiding and apparently under the influence of the "murder association" known as the Decay of Angels.
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A month after the events of Cannibalism, Tonan conducts an award ceremony for the Armed Detective Agency for their contribution to establishing civilian security. As a reward, he presents Armed Detective Agency president Fukuzawa a purifying Shikyuu Award.
Then, he overhears a discussion between two men that the Agency president is to be sent an unofficial offer to be special advisor to the police riot squad, which they think might put the Office of Special Investigations to shame. Tonan interrupts them and assures them of the Agency's competence as an organization, able to mitigate the earlier mass public insanity incident and prevent the fall of a whale-shaped warship. He believes that the Agency will become a reliable stronghold throughout Japan.
Later, Tonan comes across Atsushi Nakajima along the streets and thanks him for their services. He inquires about the progress of their investigation, but, to his confusion, Atsushi dodges his questions and immediately takes his leave. Regardless of Atsushi's apparent wariness, Tonan anticipates the Agency's impending, inevitable downfall.
At a secret meeting with other government officials, Tonan is contacted by a Hunting Dog that an Agency member has been arrested. The group becomes enthusiastic about the recent events unfolding in their favor, which shall soon achieve their end goal. He then asks for his tardy secretary to hand him the documents on Fukuzawa's assassination targets during the Great War. Knowing how hard it must be to uncover such information, Tonan asks the secretary to arrange a meeting with the informant, to which the secretary – who turns out to be Nikolai Gogol of the Decay of Angels – remotely shoots him from behind and discards his disguise. Gogol gleefully announces the Decay's interesting plan that is connected with his life and death and with the Armed Detective Agency's involvement.
Later on, Gogol holds the government officials hostage on chainsaw chairs and challenges the Agency to save them before the chainsaws activate within 30 minutes. Tonan is spared by Gogol and handed a phone to ask for help, with which Tonan voices his grudge towards the clown. Eventually, with the Agency detectives at the doorstep, the chainsaws activate before the appointed time, and Tonan witnesses Gogol's henchmen take off their hoods, who apparently turn out to be the Agency members themselves. They later find Gogol tied up on a chainsaw chair and also gets bisected like the other hostages. Tonan soon contacts the military police outside and names the Decay of Angels to be the Armed Detective Agency.