Roshutsu-Kei Mahou Shoujo: Lovely☆Lily

Seven years ago, there was a magical girl in town who fought evil. However, she has disappeared.
The main character, Hiba Airi, seems like a normal school girl. However, she is actually a magical girl enthusiast and dreams of one day becoming one.
One day when walking home from school she saw the magical mascot Shamii trying to battle an evil that is wrecking the town. She immediately volunteered to become a magical girl and was accepted. However, she skips through reading the contract clauses and found out just how different the reality of being a magical girl is from her dream. Her power comes from embarrassment.
It was too late, however, and Airi's evil - fighting days full of embarrassment and humiliation has started