Serge Entolio, a half-elf spell breaker from a magical world, possesses golden hair, deep blue or purple eyes, and a distinctive forehead marking characteristic of his heritage. He operates with his younger brother, Hasga Entolio, driven by the goal of rescuing their mother, Ela of the East, after her imprisonment and experimentation by the Church. Serge contrasts Hasga's impulsiveness with a consistently calm, collected, and friendly demeanor, often tempering his brother's reactions to Church provocations. He notably avoids harming women, attributing this to his "pure heart."

Specializing in seals and barrier construction, Serge neutralizes curses, spells, and magical constructs, posing a significant threat to magical entities. This expertise leads him to pursue the vampire sorceress Saitohimea, intending to trade her to the Church for their mother's freedom. To coerce Saitohimea, Serge and Hasga kidnap her human classmate and friend, Haruka Shigure, as leverage. Following their mission's resolution, both brothers align with Gekkou Kurenai's student council at Miyasaka High, transitioning from antagonists to allies.