"Maquia: When the Promised Flower Blooms" is a fantasy manga adaptation of the original anime film, written and illustrated by Mari Okada and Akihiko Ureshino. The story is set in a world where the Iorph, a race of ageless beings, live in seclusion, weaving their history into a fabric called Hibiol. Maquia, a young Iorph girl, is separated from her people when their sanctuary is invaded by the kingdom of Mezarte, which seeks the Iorph's immortality. During the attack, Maquia encounters a mortal human infant, Ariel, whose mother has been killed. She decides to raise him as her own, despite the challenges of her eternal youth and his inevitable aging.

As Ariel grows, Maquia struggles with her role as a mother and the passage of time, which affects their relationship. Ariel, unaware of Maquia's true nature, grapples with his identity and the societal pressures of his human world. Meanwhile, the kingdom of Mezarte continues its pursuit of the Iorph, driven by the belief that their blood holds the key to immortality. This pursuit intertwines with the lives of other characters, including Krim, an Iorph who escapes the invasion and becomes entangled in the kingdom's political machinations, and Leilia, an Iorph girl captured by Mezarte and forced into a political marriage.

The narrative explores themes of love, loss, and the passage of time, as Maquia and Ariel's bond is tested by the realities of their differing lifespans. The story also delves into the consequences of immortality and the human desire to conquer mortality, as well as the sacrifices made for the sake of family and love. Through its intricate plot and character dynamics, "Maquia: When the Promised Flower Blooms" presents a poignant tale of connection and the enduring impact of relationships across generations.