Kotetsu is a ninja agent of the United Kanto Group, operating under Tokunari Yukiya. He possesses long black hair, usually tied back, and employs round glasses as part of a timid student disguise during undercover missions. Trained in the Kouga ninja tradition, he wields advanced martial and stealth skills.

He frequently assists protagonists Yaji and Kita in combating corruption and crime within academic institutions. During the "Phantom Clan Sumeragi" incident, he intervened in attacks against Genzo Murasame, providing both combat aid and intelligence on the Sumeragi Clan. Kotetsu revealed the clan's internal strife, including stolen secret files that led to the leader's suicide and the vengeful quest by children Yosuke and Masako. His actions helped avert further conflict between Murasame and the Sumeragi assailants.

In the "Yearning for Tree Peony" case, Kotetsu delivered background information at a Jizo Bosatsu shrine concerning a decade-old conflict involving the Kendo club leader at Oukadai High School. He participated in resolving tensions around Shirotae Anenokoji and her Fusokai group, supporting efforts to dismantle their influence. His assistance proved instrumental in countering the Fusokai's activities and delivering a symbolic message to Shirotae.

Kotetsu's involvement consistently entails intelligence gathering, combat engagement when required, and offering strategic insights to resolve conflicts. His missions are typically executed under Yukiya's directives, though he operates with autonomy in the field.