Out of the blue, and in the middle of the school’s semester, Im Yoona decided to bid Australia goodbye and say hello to her beloved homeland, South Korea, where she will continue her study at one of the most prestigious schools that only the children of affluent families could manage, Shi Dae University. Not only that, she’s also planned to learn swimming just because she wants to try something new and hopefully fun, so she seek help from her older brother, Im Nichkhun, former captain of the swim club in his college days and now a young businessman.

But because of how his life became so busy since graduation, the chances of teaching her sister are slim. So he planned to have Yoona trained by his long-time friend and also the current captain of Shi Dae University Swim Club, Kwon Yuri. As a good dongsaeng for her favorite sunbae, Yuri said yes but soon regretted her decision when she couldn't take Yoona's charismatic pesky attitude anymore. The girl is a freaking choding. She always gets on her nerves, teases her to no end, and her gorgeous smile drives her crazy.

Now, how can the supposed to be cold (but y) swimmer handle her student's irresistible charm?