Lia hails directly from a supernatural realm, confirmed as an authentic devil, not a disguised human. She enters the human world via a portal, departing from her friend Selina. Her arrival is abrupt, landing squarely on Hideya's lap and startling him. Hideya initially assumes her striking appearance indicates cosplay, but Lia firmly declares her true demonic nature.

She reveals Hideya summoned her using satanic magic one month prior to grant his wishes. Feeling responsible for the delayed response, Lia insists on serving him to rectify this perceived failure. Her core motivation is to strictly fulfill the summoning's terms, regardless of Hideya's changed circumstances since the ritual.

When Hideya rejects her service—having already achieved his original wish by forming a relationship with another woman—Lia reacts with visible distress, crying at his dismissal. Undeterred, she persists. Utilizing unspecified charms and strategies, she actively works to remain a part of Hideya's life, demonstrating resilience and determination.

Her background mentions only her origin realm and her friendship with Selina; no details about lineage or wider supernatural society are provided. Her actions in the human world remain entirely focused on resolving the conflict arising from the summoning. Her character arc concludes within this singular framework.