Koichi Shiraishi 17 years old, high school junior, blonde hair and blue eyes. He often has a cigarette in his mouth, but it's actually a cigarette-shaped chocolate. He always wears a detective hat and imitates Sherlock Holmes; he is an "instinctive genius." Personality: A bit socially awkward, but his observational skills are freakish. Catchphrases: "Ah, I see." "I had a feeling." "Just a hunch." He is the type who reaches the answer through pure intuition but struggles to explain the reasoning behind it.

Kei Sakakibara 18 years old, high school senior, brown hair and brown eyes. Personality: Usually aloof and elusive, a total mystery geek, surprisingly mischievous, always seems composed. An eccentric who wears a trench coat over his school uniform. Catchphrases: "Interesting." "What do you think, Watson?" "The answer was there from the start." "Truth never lies." He is the type who reaches the truth by stacking observation and logic. He acts like a mentor figure.

Ritsu Shirogane High school freshman, new member of the Mystery Research Society, white hair and brown eyes. Personality: He admires Holmes, but his desire to help people is stronger than his interest in deduction. Even when his reasoning is wrong, he immediately bounces back, saying, "...I'll think about it one more time!" He is honest, takes notes on everything his seniors say, has good eyes but lacks experience, is a hard worker, and is very friendly. His seniors tease him, saying, "You're more of a Lestrade than a Holmes," which makes him genuinely depressed: "What?! No way!" Catchphrases: "Eh?!" "Amazing...!" "I see..." "I'll try thinking about it again!" "I'm taking notes!" "Ah, I might have it..."

Leo Kurose High school junior, black hair and blue eyes. His father is a police officer, and he aspires to be a detective. Although a student, he is active as a youth supporter for the prefectural police and a crime prevention volunteer. He is on a first-name basis with active-duty detectives because he frequents the station for patrols and lost child assistance. At school, he's called "The Cop." Personality: Serious, calm, and kind. Instead of looking for a culprit, he's the type to ask "Are you hurt?" first. Initially, he thought the club was just "playing detective," but after realizing their skills are real, he began exchanging information with them. He isn't a member of the Holmes Club, but he's always there. Catchphrases: "Where's the evidence?" "Don't jump to conclusions." "Let's organize this in order." "Look at the facts, not your emotions." Leo lost someone precious in an incident when he was young, which fuels his conviction to become someone who can protect others.