Kang Ho-gu (Choi Woo-shik) has never had a proper girlfriend, with girls constantly taking advantage of his sweet, naive nature by enjoying all the perks of dating then friend zone-ing him. His relationship-savvy twin sister Kang Ho-kyung (Lee Soo-kyung) mocks him and his best friends Kim Tae-hee (Choi Jae-hwan) and Shin Chung-jae (Lee Si-eon) for being sorely lacking in any dating skills.Do Do-hee (Uee) is an athlete on the Korean national swimming squad, and won the silver medal at the recent Asian Games. Driven and competitive, she's frustrated at never getting first place and is known for cursing a lot.The timid, bullied Ho-gu had a crush on Do-hee in their teens, when her beauty and sports cred made her the most popular girl in high school. She's the only reason he goes to their high school reunion, and when they meet again, he's surprised to learn that she remembers him....