Esmeralda, also known as Esmeralda San Valiante, is the Queen of the Valiante Kingdom and the mother of Alfonso. Her background is rooted in a secret lineage she never knew she possessed. She was born as the younger daughter of the previous bearer of the title of Garo and the sister of Anna Luis. To protect her from the Church's persecution of Makai Knights and Priests, her father arranged for her to be taken as an infant and adopted into an aristocratic family. Raised far from the world of magic and horror, she lived a life of privilege and eventually married King Fernando Valiante, with whom she had a son, Alfonso.

As a character, Esmeralda is defined by her quiet strength, dignity, and deep maternal love. She is a composed and regal figure who prioritizes the safety and future of her son above all else, even her own life. Her primary motivation is to protect her family and her kingdom from the treacherous machinations of Mendoza, the royal advisor. After Mendoza orchestrates the king's poisoning and falsely accuses Esmeralda of both the crime and infidelity, claiming Alfonso is an illegitimate child, she is imprisoned and sentenced to death for treason. Her driving goal becomes not her own survival, but ensuring that Alfonso escapes and becomes strong enough to reclaim their home.

In the story of Garo: The Animation, Esmeralda serves as a crucial emotional anchor and a catalyst for Alfonso's quest. Her role is largely defined by her suffering at Mendoza's hands and the ultimate sacrifice she makes. While imprisoned, she is kept alive by Mendoza specifically to be used as a bargaining chip to control her son. Demonstrating immense resolve, when she learns that Alfonso has returned, she chooses to take her own life using a broken plate, ensuring she cannot be used as a weapon against him. This tragic act solidifies Alfonso’s determination and removes the primary leverage Mendoza holds over him.

Her key relationships are central to her identity. She is the devoted wife of the ailing King Fernando and the loving mother of Alfonso, for whom she keeps a cross pendant given to her as a baby, believing it to be a protective charm. Unbeknownst to her, this pendant bears the Garo emblem and is a link to her biological father. This connection, which she never learns, also makes her the aunt of the protagonist, Leon Luis, as her sister Anna was his mother, though she witnesses Anna's execution without ever recognizing her as family. Her primary antagonist is Mendoza, who recognizes the significance of her pendant and destroys her life to eliminate the threat her son could pose to his power.

Esmeralda does not undergo a significant transformation throughout the series in the sense of changing her beliefs; rather, the situation forces her latent strength to the surface. She begins as a queen living a privileged, if politically delicate, life. Her development is the journey from a protected noblewoman to a prisoner facing death, and finally, to an active agent who chooses her own end to ensure her son's victory. A notable, though passive, ability is her lineage as a descendant of a Makai Knight, which is passed down to her son Alfonso, enabling him to inherit the armor of the Knight of Light. She herself possesses no magical or combative abilities, but her strength of will and her final act of self-sacrifice are her most defining and powerful actions.