Zettai Meikyuu Himitsu no Oyayubi-hime

Charlotte is a young girl who lives in a small village out in the countryside. She happily spends her days with her childhood friend and next-door neighbor, the Little Match Boy.

One day, she suddenly shrinks to about the size of a thumb. With her cute and fairy-like new body, Charlotte immediately gains popularity. People begin to call her "Thumbelina."

One day, while Thumbelina and the Little Match Boy are off on a trip to a distant spring, the village is attacked by mysterious soldiers. Knowing that they are searching for Thumbelina, the Little Match Boy takes her into the depths of the forest to protect her.

And so the two of them embark on a journey to find a way to restore Thumbelina to her normal size, all the while avoiding the pursuing soldiers. Along the way, they will make friends with a cast of colorful characters, and this adventure will reveal their deepest secrets...

(Translated from the official site)