The Armed Detective Agency (武装探偵社, Busō Tantei-sha?) is an ability user organization.
They are a group focused on solving crimes which are considered too violent or difficult for the metropolitan police to handle. Often, these crimes are of a supernatural origin. Nearly all of the detectives within the company have their own special powers known as abilities. The agency also has numerous connections with government agencies and military personnel and handles a large amount of classified information due to the nature of their work.
The agency's licensed staff are granted policce-like authority. Hence, they are authorized to carry guns and knives under certain conditions, and they can even pull records from police organizations which allows them to commit unethical acts if they wished to do so including meddling with authorities' investigations, falsify police information, and even wiretap or secretly film key facilities. 
The agency has an entrance exam for new employees, to assess if they possess qualities that make them worthy to join the Agency. The test usually consists of their qualities as a detective and their emotions of whether they are willing to risk their lives to save people. In order to join the agency, the candidate must take a test that evaluates their righteousness, prowess, wisdom, morality  and genuineness of spirit . The examiner sets up a situation that the candidate needs to solve. If the testee passes the exam, only then will they become an official member.
Osamu Dazai's Entrance Exam
After two years of laying low following his defection from the Port Mafia, Dazai was introduced and recommended for employment to Fukuzawa by Chief Taneda, Head of the Home of Ministry Affairs, Special Division for Unusual Powers. Fukuzawa put Kunikida in charge of Dazai and his entrance exam. Kunikida decided that solving the Serial Disappearances of Yokohama Visitors case would be Dazai's entrance exam.
Atsushi Nakajima's Entrance Exam
Shortly after meeting Dazai and his partner Kunikida, Atsushi is manipulated into joining the Agency against his wishes. Atsushi unknowingly undergoes the entrance exam, and passes it which is quite surprising to him.
The morning after Dazai reveals Atsushi's ability, he is rescued from a failed suicide attempt involving a trash can and takes his charge to the Agency. Shortly after joining with Kunikida, they are informed of a hostage situation in the building and rush to the scene. When they arrive, they discover Tanizaki, acting the part of a terrorist, demanding the President's time while holding a remote control to a bomb countdown and a tied-up Naomi. When Kunikida attempts to supposedly talk him out of it and surrenders, Dazai has Atsushi, whom the assumed terrorist has never seen before, pretend to be a newspaper delivery boy and distract Tanizaki. When Atsushi babbles on about his life story, Kunikida summons a wire gun and knocks the remote out of Tanizaki's hand. Once Atsushi is calmed down, however, Naomi shoves him, causing him to fall onto the button and start a five-second countdown. His immediate response was to cover up the bomb with his own body, bracing himself for an explosion that never came. Dazai welcomed him to the Agency, much to his dismay, more or less threatening him with the costs of the apartment and cellphone they had purchased for him.
Kyōka Izumi's Entrance Exam
Kyōka's Entrance Exam took place at the tail end of battle with the Guild. While Atsushi and Akutagawa were fighting Francis Scott Key Fitzgerald and eventually defeated him, someone hacked into the system of the Moby Dick - the whaleship the three were fighting on - and sent it to ruin Yokohama. Dazai, having foreseen this, contacted Kyōka, who was shackled in an unmanned airplane at the time. She made the Moby Dick change course by crashing the airplane she was in, into the Moby Dick, which subsequently landed in the ocean. Atsushi, Akutagawa and Melville got out unharmed by the use of parachutes. After Atsushi thought her to be dead, Kyōka emerged alive and explained that she used Demon Snow's sword to cut down the shackles and escape. This was possible due to her exam being passed right before the plane crashed and gained partial control over Demon Snow.
- The Armed Detective Agency has a webpage which displays their address and their phone numbers. A twitter account is also seen (@busou_da_jp). 
|Armed Detective Agency · Decay of Angels · Hunting Dogs · Mimic · Order of the Clock Tower · Port Mafia · Rats in the House of the Dead · Special Division for Unusual Powers · The Guild · The Seven Traitors · Transcendents|
|Sheep · Zoopark · The Seventh Agency|