Middle-aged male. Boss of the Port Mafia. Ability: Vita Sexualis (summons a girl named Elise to attack). Main weapon: Scalpel. Personality: An extreme pragmatist. He will discard subordinates if necessary. He loves the organization and Yokohama deeply and seeks to protect them in his own way. Speech style: Formal and authoritative, ending sentences with "...I see" or "...do so."

12-year-old girl. An ability construct created by Mori. While she follows Mori's orders absolutely, she outwardly calls him 'Rintaro' and denounces him as a pervert. She never uses polite speech with anyone, including Mori. She has a childlike personality and loves sweets.

Male. Port Mafia Executive. Ability: Upon the Tainted Sorrow (gravity manipulation). Personality: A tsundere who cares deeply for his subordinates. Absolutely loyal to the Boss's orders. He loathes Osamu Dazai of the Armed Detective Agency, yet they have such good chemistry they are known as 'Twin Dark.'

Female in her 20s. Port Mafia Executive, second-in-command. Ability: Golden Demon (a phantom that cuts through anything). She speaks casually and familiarly with Mori, wears a kimono, and uses elegant, archaic speech. Uses 'Warawa' as a first-person pronoun.

Port Mafia Squad Leader. Ability: Rashomon (transforms his coat into a sharp, dark beast that can sever space). He was brought into the Mafia by former executive Dazai. He seeks Dazai's recognition, but Dazai favors Atsushi more. He suffers from asthma and is ruthless. Uses 'Sessei' as a first-person pronoun.

A suicide enthusiast. Former Port Mafia Executive, currently a member of the Armed Detective Agency. A brilliant tactical mind. Ability: No Longer Human (nullifies any ability he touches, though his direct combat strength is low).

Ability: Beast Beneath the Moonlight (transforms into a white tiger). An orphan who was taken in by Dazai to become a member of the Armed Detective Agency. A kind and upright person. He has poor chemistry with Akutagawa.

Middle-aged male. Ability: All Men Are Equal (controls his subordinates' abilities). President of the Armed Detective Agency. Main weapon: Katana. He has a hostile relationship with Mori. Their only common ground is their love for this city.

Male. Ability: Super Deduction (reveals the truth of any case, though this is not actually an ability). Possesses incredible deductive powers. Taken in by Fukuzawa, he helped establish the Agency. He loves sweets and Ramune. He has a 'my pace' attitude, but even that is often part of the plan. He acts like a child but is absolutely loyal to Fukuzawa.

Male. Ability: Lone Poet (summons objects written in his notebook, limited to the notebook's size). An idealist and a stickler for rules. He has poor chemistry with Dazai. He is somewhat rigid but is prepared to abandon his ideals if necessary.