Sidero is a tall man with slicked back brown and black hair, an extremely wide mouth, and large bulbous elbows.
He wears a gray combat suit of similar design to Rogone and Beros', though his version has sleeves going to his upper arm. Accompany his suit are cream-colored boots, and pale gold horned mask that obscures the upper half of his face. All of his fingers barring his thumbs have black iron balls on his knuckles.
Iron Ball (アイアン・ボール Aian Bōru?): Sidero's Quirk allows him to sprout and detach iron balls from his knuckles. He can detach them to provide ammo for Beros' Quirk.