Emma Guzmán is an independent Makai Alchemist who strategically embraces the label "witch," allowing herself to be captured to infiltrate enemy strongholds. She exhibits a bold, brash personality, maintaining composure and sarcasm even under pressure. Her background includes marriage to fellow Makai Alchemist Luciano Guzmán, who succumbed to possession by the Horror Arabel. After this, she vowed to personally end his suffering, deepening her distrust of the Makai Order following her own imprisonment over fears she might transform into a Horror. This experience cemented her view of Makai Knights as arrogant, particularly in their underestimation of her combat abilities as a woman.

Trained in Makai alchemy, she specializes in physical combat enhanced by acrobatics and alchemical techniques. Her primary weapon is a Madō Wire, a mono-molecular strand crafted using her alchemical formula, used to ensnare targets, erect barriers, and cast spells. She deploys the wire with a gun-shaped Madō Wire Launcher, equipped for firing long-range energy bolts and rapid-fire magical projectiles. She also employs a Madō Bell to expose Horrors and previously used Madō Bagua Tags for concealment.

Her path crosses with protagonists León Luís and Germán Luís when they rescue her from Mendoza's inquisitors. Despite her general disdain for Makai Knights, she repeatedly aids them, showing particular concern for León. She recognizes the significance of his bodily markings as a powerful seal and expresses remorse after inadvertently revealing his inexperience in intimate matters. After fulfilling her vow to defeat Arabel and free Luciano's spirit, she shares a brief romantic encounter with León. She typically departs without formal farewells, as seen after the defeat of Mendoza and again following the Sir Venus incident.

Years later, during the Divine Flame events, she reunites with the group to investigate the Horror Nigra Venus at Vazelia. Partnered with Prince Alfonso San Valiante, she infiltrates the lake kingdom and intervenes to save Alfonso from Nigra Venus's attack. She later aids in protecting the child Roberto and assists León in the final confrontation by facilitating the combination of the Garo and Zoro armors into a unified form. Her actions extend to preventing León's attempted self-sacrifice against Mendoza, physically holding open a portal to ensure his survival. This period demonstrates her continued, episodic alliance with the Makai Knights and commitment to resolving supernatural threats. Following the Vazelia incident's resolution, she departs unannounced once more. Her narrative concludes with a parting from León that suggests future encounters, reflecting her transient yet reliable episodic presence in their missions.