Once upon a time, four girls lived together in dorms and formed a group called Mamamoo. The youngest member, Hwasa, unlike the other members liked to stay at home so she always did chores while everyone went out. But don't misunderstand, even if she was the youngest, she did and said everything she wanted to the older members. Her nickname was Hwa Sassy and nobody could tame her. She had her own room whereas Moonbyul and Wheein had to share one.

One day, the King Kim Do Hoon decided to organize a costume ball to choose a fiancé for the Prince Key. Every young lady in the WA Kingdom was excited and prepared themself for that occasion even Hwasa. She always wanted to go to a ball and that moment happened. Actually her members didn't want her to take part because they thought she would scare the Prince and it would bring their group a bad reputation so they came up with an excuse few hours before the ball. As she was in charge of chores, she couldn't protest against it. While everyone went to the ball, she cleaned for hours until she saw a light before her. That was a fairy, she couldn't believe it.

A fairy named eSNA offered her help. She was her Fairy Godmother and to show her good will, she did the rest of the chores. Then a magnificent red dress and a pair of glass slippers appeared and she gave it to Hwa Sassy and turned a pumpkin into a golden carriage, mice into horses, a rat into a coachman, and lizards into footmen. Her Fairy Godmother told her to return before midnight or everything would return to their true aspect. Hwa Sassy thanked her and went to the costume ball.

As she entered, everybody looked at her. She even got invited by the Prince Key and they danced together without saying a word. It was her most memorable night but she had to leave before midnight.

The next morning, her members talked with enthusiasm about the ball and the mysterious lady who captivated the Prince. Hwa Sassy listened to them silently and grinned at she thought of that night.

At the castle, the Prince asked his father to organize another ball. He fell for that mysterious lady with the red dress. The King seeing his enthusiasm, made an announcement for an other ball.

Again, every young lady prepared herself to go there. Hwa Sassy saw that opportunity and waited for the night to come. Her group members didn't have to look for an excuse again as she faked to be sick. When they left, her Fairy Godmother came to her and did everything like the last time.

At the ball, Hwa Sassy danced again with the Prince Key and they started to talk.

“You're beautiful tonight.”

“Tonight ? I guess I wasn't yesterday.”

“I mean, you're prettier than yesterday and you are kind of wild.”

“But don't you like it ?”. She gazed at him like she was looking into his soul.

“I don't, I love it. You are interesting, milady.”, he answered with a sweet smile.

“You're not bad neither.” She retorted.

They kept dancing and talking so much that Hwa Sassy forgot the time. It was nearly midnight and she had to go home. She was dancing with Prince and suddenly ran outside. Prince Key went after her but he only found one of her glass slippers. Hwa Sassy came back home with only one slipper but strangely it didn't disappear.

He kept it and announced the day after that he would marry to whom it belonged. His guards and him went in every house to find that mysterious but it fit nobody. Then, they came to Mamamoo's dorms and the three members tried it but their feet were too big. There was only Hwasa but the older member protested saying that she never attended the costume ball. The Prince didn't listen to them and asked Hwasa if she could put that glass slipper on. In response, she said:

“I need a freakin shoe. You know it.”

The Prince laughed at her answer and gave her the glass slipper. She put the other one on to confirm her identity. Few days later, they announced their marriage and her and her members could also perform in various stages in the kingdom.