Oh Jung Se and Ryu Hyun Kyung play the main couple in their 30s who chose to live together instead of getting married, and have been sharing an apartment for two years. Oh Jung Se plays a voice actor and Ryu Hyun Kyung plays a reviewer who runs a blog. Choi Yeo Jin and Jung Joon Young have been cast as the second couple — they’re twelve years apart in age and have been living together for a year. He’s a pretty-boy singer who carries his guitar everywhere he goes, but doesn’t actually know how to play it all that well. She’s a penny-pinching ajumma in the body of a hot woman who basically supports her much younger boyfriend. He drives her crazy but he’s a good guy at heart, and she can never manage to stay mad at him for long. Ha Eun Sul and Park Jong Hwan play a 20s couple that just moved in together. She’s the type of woman who doesn’t want her boyfriend to know that she isn’t the perfect embodiment of femininity, and works tirelessly to keep up the illusion. Lee Jae Joon plays a loner who prefers to stay at home, but is forced to get a roommate for financial reasons. He doesn’t even want to exchange unnecessary small talk with the guy, and thus seeks out a foreigner who can’t speak Korean very well. Terada Takuya plays the new roommate, a young man from Japan who’s on a trip around the world. Takuya thinks it a shame that Lee Jae Joon is wasting his youth as a homebody, and begins to draw him out into the world.