No Breathing (2013)

Woo Sang is a national swimmer who's always pursuing the number one spot. Won Il is a swimming prodigy who stopped participating in the sport, and now wants to make a comeback. Not only do they become rivals, but they also fall for the same girl, Jung Eun, an aspiring musician who is their childhood friend. The three lifelong friends suddenly find themselves having to juggle love, friendship, and competition, as they undergo the rite of passage of growing up.