Ga Ran and Nam Joon used to be classmates in elementary school. Ga Ran, a tomboy, that prefers trousers to skirts and loves to perform taekwondo rather than to play piano. Nam Joon on the other hand is a Mr. Perfect, who cares all about looking good, having a fine brain and to be popular in school, especially among the girls. One day, Ga Ran sees Nam Joon giving away sweet bun, which Ga Ran's friend gave him, to another girl. Ga Ran beats Nam Joon up and their rivalry lasts throughout the entire high school period. A few years after college, Ga Ran and Nam Joon meet again as adults, both recovering from recent break-ups. Despite their constant bickering, they gradually realize that they're meant to be.