Saimu Mahou Shoujo Kureca Riboca

Sasara Sawajiri, a third-year high school student, makes a contract with a mysterious creature called "KureKure" to cure her beloved younger sister's illness, becoming a magical girl who defeats monsters controlled by malicious intent. Sasara spends her days fighting monsters as a magical girl, but there's a huge catch in that contract… (Source: Leed, translated)