A seventeen-year-old ordinary girl, Lee Jung Ah, was searching for a purpose in her life. After years of living in an orphanage, she had learned how to be independent. In one of her part-time jobs, she met a man who took interest in her hardworking self. Having to tell her story to the man, the man was impressed. But what if the next day, the man came back offering to adopt her? All things are going well already until Jung Ah found herself in front of 12 boys and the man who adopted her introducing them as her brothers from that day onwards.

In certain circumstances, Lee Jung Ah's new father was put in a situation in which he needed to leave her with her 12 brothers for a long period of time. What will she do when the boys start to show their dislike towards her?

Or in certain circumstances too, the dislike turns the other way around?