Shoujo Tenshi Milcute

Japanese Title: 少女天使みるきゅーと

Plot
Miu Amano owns a box that her father gave to her five years ago just before he left. Every year on her birthday, he sends her a postcard, but this year is different. This year he sends a present—a key that fits the box’s lock perfectly. Inside the box is a small device that transforms into a tiny cat that calls itself “heaven’s cat”, Francois d’Mielle the third. He tells Miu that her father gave him an assignment—to turn Miu into an angel Shoujo Tenshi Milcute and save the world!