La Suite D'amour Du Chat Noir

La Suite D'amour Du Chat Noir (黒猫恋愛組曲, lit. "Black Cat's Love Suite") is a manga series by Satoru Takamiya. It was serialized in Ciao.

Plot
Have you heard of the world where a witch and her black cat live happily together? It's a paradise where nothing bad happens and no one gets sad. But then, the witch dies and the cat is left alone. Somehow, she [the cat] appears to become human. What is the fate of the black cat who searches for her witch in the human world?