Nahyun, who is afraid of water and unable to swim, begins taking swimming lessons in an effort to conquer her fear. During these lessons, she encounters Cha Jaehwan, a charming and muscular swimming instructor known for his questionable reputation. Initially drawn to him, Nahyun soon retreats, thinking that some men are simply beyond her reach. However, when this "unreachable tree" reveals a surprisingly generous side, she impulsively suggests a one-night stand. What ensues is a clumsy, rumor-laden romance that takes an unforeseen twist when Jaehwan asserts that she was his first.