The story begins when a middle school girl named Yume sees something fall from the sky, and meets a pale violet-colored kitten named Mew. It turns out that Mew has the power of "Yume Synchro" (Dream Synchro), the power to enter dreams. In the dream world, the girl and Mew collect Dream Stones.

In the previous series "Kite," a killer—Sawa—suddenly disappears after she avenges her parents' death, and no one knows where she is. Several years later, a figure dances airily on the dark side of a big city. She is an angel of death, killing her victim gracefully and disappearing. Monaka is a normal high school student, though this quiet and modest life has a darker side. An angel of death is Monaka's other persona.

The series is set in a near-future world where the boundary between human being and AI is vague. A rapid biological evolution, similar to "Cambrian Explosion," is caused by one incident. This incident turns into the genesis of a new jostle for supremacy, and the influence of the evolution goes beyond biological framework and spreads to various kinds of materials and technologies. The era of massive evolution involving diverse existences, such as human, machines, and biotechnologies, is coming. Characters fight an existential war in such a world. (Source: ANN)

In the Kagami household, the old Western palm-sized mirror has been passed from from generations to generations. Akko-chan has been taught about the importance of the mirror and when she finally receives it from her mother, she cherishes it with all her might. One day, in the midst of a disturbance made by Taishou and his gang, Akko-chan accidentally broke the mirror. She made a grave and buried the broken pieces in the backyard. That night, Akko-chan was awakened by a flash of light and a kind voice which belongs to the Queen of the Mirror Kingdom. The Queen expresses her gratitude to Akko-chan for valuing the mirror so much and offers her a gift—a magical compact mirror. Whenever Akko-chan sings the magical words, she will transform into anything she wants. (Source: ANN)