Ema Guzmán is an independent Makai Alchemist, distinguished by her intelligence and boldness. She willingly embraces the term "witch" and once allowed her own capture to infiltrate enemy territory. Despite enduring harsh treatment from her captors, she remains calm and verbally defiant. She demonstrates considerable skill in physical combat, incorporating acrobatics and magic into her style, a rarity among her peers.

She was married to Luciano Guzmán, a fellow Makai Alchemist who became possessed by the Horror Arabel, leading Ema to vow his defeat. She harbors a distaste for Makai Knights, whom she perceives as arrogant and dismissive of her capabilities as both an alchemist and a woman. This sentiment originated from her mistreatment by Order members who imprisoned her after Luciano's transformation, fearing she might also succumb to darkness. She later learned none of those tormentors survived their encounter with Arabel.

Her relationship with León Luís is complex, marked by a playful and teasing attitude, though she shows concern for him. After assisting León in defeating Arabel, an act that brought her closure, she engaged in a one-night stand with him. Following the final battle with Mendoza, she parted ways with León and Alfonso San Valiante to return to her hometown. She later rejoined the group during the events involving the Horror Nigra Venus but departed again without notice after its defeat.

Ema employs a Madō Wire, a mono-molecular wire launched from a specialized gun-shaped spindle, which serves as a weapon, grappling hook, and a focus for spells and energy attacks. She also uses a Madō Bell to expose Horrors and formerly utilized Madō Bagua Tags for concealment.

During the incident involving the Horror Nigra Venus, Ema was assigned to investigate Vazelia alongside Alfonso. She saved Alfonso from an attack by the Horror and assisted in the rescue of Roberto, Germán Luís's son. She fought alongside León and others to thwart the plans of Dario Montoya and the Horror.