Once known for ruling her school with a single punch, Mina is a fiercely righteous girl who lost her parents in a childhood accident and was raised by her aunt. Entering high school with a promise never to fight again, she hopes for a normal fresh start but finds herself drawn to her seatmate Min ki from the very first day. When Min ki becomes the target of Se hyeok, the leader of a delinquent clique, Mina intervenes by rescuing him while disguised in a tracksuit with her face covered. The incident throws the school into turmoil as students search for the identity of the mysterious rescuer and Min ki begins his own pursuit of the truth. As tensions rise around Min ki, Mina struggles to hide her identity while maintaining an increasingly unstable everyday life.

Kim Ha Yeon is an ordinary 18-year-old girl who dreams of a life as dramatic as the ones she sees on screen. Her life takes an unexpected, mystical turn when she heads to the unfamiliar countryside village of Upo-ri for her summer break. There, she crosses paths with Jo Yu Gyeom, the heir to a traditional noble family, and his girlfriend, Sae Ryeong. While he possesses stunning looks and a genius talent for swimming, he lives a colorless existence constrained by old-fashioned rules and repetitive routines. As these two opposites meet in the quiet beauty of Upo-ri, their worlds collide, sparking a transformation in their daily lives and the beginning of a once-in-a-lifetime summer.