Sōshirō Anehara is the younger brother of Misa Anehara, a supremely powerful modern magic user. His birth resulted in their mother's death due to magical energy depletion from saving Misa years prior. Consequently, Misa raised Sōshirō herself. Constant exposure to her magically enhanced cooking during his upbringing granted him complete immunity to all magic. This immunity renders him unable to perceive magical phenomena, fueling his persistent skepticism about magic's existence despite witnessing inexplicable events like spontaneously appearing washbasins.

He possesses a sensible, serious, and pragmatic personality, consistently acting as the voice of reason against his sister's eccentric and common sense-defying behavior. Sōshirō primarily manages household chores and maintenance at their residence. He frequently admonishes Misa for her impractical actions while simultaneously demonstrating deep concern for her well-being. His unique magic immunity occasionally leads adversaries to mistakenly believe he is a trained agent of the Church Militant, though he has no affiliation with such organizations.