Yuu Morisawa is an ordinary 10-year-old girl granted magical powers after aiding an alien named Pino Pino in returning to his home world, Feather Star. As a reward, she receives a magic wand enabling her to transform into a 16-year-old version of herself, Creamy Mami, for one year. Two cat-like aliens, Posi and Nega, guide and oversee her use of magic.

Using this transformation, Yuu adopts the Creamy Mami identity and becomes a popular idol singer following an impromptu television performance. She juggles her ordinary life—attending school, helping at her parents' crepe shop, and harboring a secret crush on childhood friend Toshio Ōtomo—with her burgeoning idol career. Toshio develops feelings for Creamy Mami unaware she is Yuu, creating tension. Yuu's secret faces multiple near-exposures, including an incident where Toshio witnesses her transformation. This forces a journey to Feather Star to restore her powers by erasing his memory.

In the OVA *Majokko Club Yoningumi: A Kuukan Kara no Alien X*, Yuu teams up with other magical girls—Persia, Mai, and Yumi—to battle an alien monster transforming young women into elderly hags. As Creamy Mami, she joins a space mission to confront this threat, applying her magic within a science-fiction setting.

Her character extends into crossover media. She battles the magical girl Minky Momo in the *Magical Angel Creamy Mami Long Goodbye* OVA and appears alongside characters Magical Emi and Persia in *Adesugata Mahou no Sannin Musume*.

Throughout her adventures, Yuu maintains a spirited, optimistic personality. She navigates challenges of secrecy, responsibility, and adolescence, often relying on Posi’s encouragement and Nega’s caution. Her magical journey concludes after the year ends, though her legacy as Creamy Mami continues in collaborative specials and crossovers.