ねこ・ねこ・幻想曲

"Shiro" is a black cat who loves her family very much. She loves them so much she wants to help them out in times of need and trouble…but it’s difficult to do this if she's just a cat. So one night, she wishes on the moon to make her able to help, and the next day, she has turned into a human girl.

(Source: AniDB)