Mercelída Ygvar reigns as Queen of Ygvarland, a succubus-governed kingdom within Álfheimr. Sustained by sauzfryma, she maintains a 3,000-strong harem for nourishment. Her appearance features long blonde hair, green eyes, pointed ears, a tail, and a curvaceous figure.

The youngest daughter of Queen Ísalind, Mercelída fled to the human realm amidst a deadly throne conflict between her sisters. There, at eighteen, she encountered the thirteen-year-old Naoya Tohara. Their sexual encounter, intended to replenish her strength, conceived their daughter Asuha. Mercelída later returned to Álfheimr, claimed the throne, married a king, and bore a second daughter, Astarotte Ygvar. Seven years after Asuha's birth, she returned the child to Naoya's care in the human realm, seeking to protect her from royal intrigues.

Outwardly playful and promiscuous, Mercelída often favors her harem and personal indulgences over duties. Yet she deeply cares for her daughters and Naoya, regretting her role in causing Astarotte's severe fear of men. This fear stems from Astarotte witnessing a man entering Mercelída's bedroom as a young child, an event resulting in lasting trauma. Despite distancing herself to avoid complicating Naoya’s bond with Astarotte, Mercelída holds romantic feelings for him, fondly calling him "Darling" and recalling their past.

Her relationship with Astarotte was strained by the childhood incident and Mercelída's frequent neglect, like tardiness at school events. They gradually reconciled through heartfelt talks. With Asuha, Mercelída maintains a maternal connection, discreetly spending time together when Astarotte is away. She shares a close bond with her bodyguard Úrsúla, who serves as both protector and favored lover. Mercelída rules with a blend of approachability and wisdom, earning her subjects' respect despite occasional administrative reluctance.