Bunzou Aoki serves as a detective in the Tokyo Metropolitan Police Department’s Investigation Division, distinguished by his sincerity, physical courage, and reserved nature. A former Navy kamikaze pilot during World War II, he survived the conflict when his mission was preempted by the war’s end—an experience that forged his disciplined resolve and informs his approach to justice. His career weathered setbacks, including a temporary demotion to the Edogawa branch following "The Painted Buddha Banquet" incident, though his heroic actions during the "Demon Drip" event swiftly reinstated him to his post within six months.

Possessing a youthful, almost boyish visage with a prominent head and robust frame, Aoki’s unassuming appearance belies a rugged physicality. Polite and principled, he navigates investigations with honesty, though high-stakes scenarios occasionally trigger impulsive acts, such as direct confrontations with suspects. He holds quiet reverence for his former partner, Shutaro Kiba, whose investigative philosophies he admires despite Kiba’s dismissive attitude. Similarly, his restrained affection for colleague Atsuko Chuzenji remains unvoiced, tempered by professional propriety.

Aoki’s skepticism of hereditary privilege in professions underscores a broader critique of societal structures, challenging assumptions that lineage ensures competence. His survival as a kamikaze pilot and career adversities color his contemplative views on duty and mortality. Proficient in martial arts yet vulnerable to alcohol’s swift incapacitating effects, he balances capability with fragility. His tenacity drives his involvement in a pivotal dismemberment case, though his aggressive tactics—evident in clashes with figures like Kōshirō Mimasaka—skirt recklessness. While his parents reside in Sendai and he lodges in Suidobashi, these personal threads remain secondary to his professional pursuits. Fictional accounts occasionally align him with colleagues Toriguchi Morihiko and Noriyuki Masuoka under the moniker "Three Fools," highlighting his role within investigative camaraderie.