Tetsuro Tetsujin forms one half of the Iron Brothers alongside his twin brother, Tetsuo. As the older twin, he shares a close bond with Tetsuo. The pair sport identical sailor suits and metallic helmets, a distinctive look central to their identity. They proclaim these helmets grant psychic abilities, including flight and space-time travel, but state the powers remain unusable while worn to evade military detection—a condition that inadvertently prevents their activation. No verified demonstrations of these powers occur.

Their shared history includes being laboratory guinea pigs, though specifics of the experiments or institution remain undisclosed. Within the Arakawa river community, they address Stella as "Boss," indicating a subordinate relationship. Functionally, the Iron Brothers maintain and manage the village's hot baths, utilizing repurposed oil barrels. They nurse envy toward Kou Ichinomiya due to his connection with Nino, often reacting with petty or mischievous behavior. Their interactions typically position them as comic foils, defined by their helmeted appearance and extravagant claims.

Their roles remain consistent as supporting figures focused on communal tasks and light antagonism fueled by envy. Official media documents no significant character development or evolution. Background elements, such as family origins or life preceding the laboratory experiments, are unexplored.