From Nagareboshi:
Miu's father left her five years ago with a box. The box was locked, and Miu's father took the key with him. on her birthday, he sent it back, and inside the box was a mahou shoujo transformation device! Now it's Miu's job to transform into Shoujo Tenshi Milcute and save the world!

EDIT: The author is putting this series on hold because she wanted to start Modotte! Mamotte Lollipop.