Shirō Magi holds the position of second-in-command in the organization P.A.N.D.R.A. He typically sports long, untamed black hair and a stubbly beard—features maintained through continuous carbon manipulation training; without it, his hair shortens and his face becomes clean-shaven. Magi frequently appears in a black business suit.

Diligent and serious, he contrasts with other P.A.N.D.R.A. members. His fierce loyalty to leader Kyousuke Hyōbu drives him to frequently reprimand Hyōbu for neglecting duties or causing disruptions with pranks. This devotion originates from childhood: Hyōbu rescued Magi and Momiji Kanō from a helicopter attack in a war-torn region. Recruited as a child, Magi has followed Hyōbu ever since, addressing him as "Major" and rarely challenging his decisions. Magi recruited most P.A.N.D.R.A. members and is implied as the first recruit.

Initially distrustful of The Children—particularly Kaoru Akashi—Magi later acknowledges her perspectives, especially regarding Feather's Hyōbu clones created after conflicts involving Gilliam and Black Phantom's Yuri clones. His abilities involve atomic-level carbon manipulation within his body, channeled through psychokinesis to weaponize his hair. He forms bulletproof shields, creates steel-piercing blades, and generates flight-capable wings.

As second-in-command, Magi prioritizes P.A.N.D.R.A.'s stability and objectives, often mitigating operational challenges amplified by Hyōbu's unpredictability. His foundational bond with Hyōbu is defined by unwavering dedication to their shared goals. Throughout official portrayals, his loyalty and pragmatism remain consistent, with his evolving acceptance of Kaoru marking a significant shift in his interactions.