Himitsu no Akko-chan 3 Episode 21

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: Anime News Network)