Baron Kaidō is the headmaster of Root Gakuen High School, attended by Kaito Daimon and other main characters. Following the death of Kaito's parents, who were P.O.G. officers training him as a Phi Brain candidate, Baron Kaidō assumed legal guardianship of Kaito. He enrolled Kaito at Root Gakuen, positioning him to encounter the Orpheus puzzles and the conflict with P.O.G.

Within P.O.G., Baron Kaidō serves as section-chief of Section Φ, an autonomous division. He opposes the organization's increasingly lethal direction, specifically its use of philosopher's puzzles designed to kill Solvers rather than test intellect. This stance positions him at odds with P.O.G. factions advocating ruthless methods. To counter this shift, he recruits Souji Jikukawa (Newton) into Section Φ and strategically guides Kaito and his allies toward the Puzzle of God, aiming to uphold P.O.G.'s original standards of puzzle-solving integrity.

His actions, including disobeying P.O.G. directives and protecting Kaito's group, ultimately lead to his arrest by the organization, stemming from his refusal to comply with orders violating his principles on non-lethal puzzles.

Baron Kaidō's involvement in Kaito's past extends beyond guardianship. Flashbacks suggest he played a role in events preceding the series, including circumstances surrounding Kaito's parents and their connection to P.O.G.'s objectives. His motivations appear rooted in maintaining a balance between P.O.G.'s foundational goals and ethical puzzle creation, positioning him as a figure attempting to mitigate the organization's shift toward antagonism.