Doppo Kunikida serves as a core member of the Armed Detective Agency, defined by intense discipline and idealism. He lives by strict schedules and efficiency, meticulously documenting his guiding principles in a notebook titled "Ideals." This notebook is also the conduit for his ability, "The Matchless Poet," enabling him to materialize any object written within its pages—provided it fits the notebook's dimensions and he comprehends its mechanics. He commonly manifests weapons like pistols, wire guns, and flash grenades, alongside utility items such as keys or stun devices, and can remotely activate pre-written pages for tactical support.

Professionally, Kunikida functions as the agency's de facto operations manager, handling logistics and mentoring newer members like Atsushi Nakajima. He fiercely protects the agency's reputation and mission success, occasionally advocating pragmatic choices, such as initially opposing the rescue of high-risk individuals like Kyoka Izumi to avoid endangering the group. Despite this, he displays deep loyalty to colleagues, respecting Dazai's strategic mind and Ranpo Edogawa's deductive skill, even participating in upholding the fiction of Ranpo's "Super Deduction" ability.

Kunikida's past includes teaching algebra at Shin-Tsuruya Institute, a career he abandoned after the Azure Apostle case to commit fully to the agency. This case profoundly impacted him; failing to save kidnap victims and witnessing the deaths of informant Rokuzo Taguchi and perpetrator Nobuko Sasaki steeled his resolve to uphold his ideals against the world's harshness. His idealism faces constant tests, like during the Hunting Dogs arc where he battles guilt after the agency is framed for terrorism. Confrontations with antagonists such as Saigiku Jono challenge his worldview, pushing him toward pragmatic sacrifices like using his own body as a decoy in explosions to shield colleagues. He suffers severe injuries in these conflicts, including loss of limbs, recovering via Akiko Yosano's ability.

In the comedic spin-off *Bungo Stray Dogs Wan!*, Kunikida's traits are exaggerated for humor. His rigidity and exasperation surface in slice-of-life scenarios, reacting to Dazai's antics during magic lessons or office chaos. These moments cast him as the "straight man" against the cast's eccentricities, while his underlying dedication to order and camaraderie persists.

Kunikida's character evolves from unwavering idealism toward a more nuanced perspective. Haunted by early failures like the Azure Apostle case, later crises—such as imprisonment following the Decay of the Angel's framing—force him to reconcile his principles with the cost of protecting others. His final stance emphasizes using his life as "fuel" for his ideals, signifying growth into resilient pragmatism anchored to his core values.