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.
Room 609: Oh Do Shi and Ryu Du Ri, started live together 2 years ago after dating for 5 years. Do Shi is a voice actor and Du Ri is an internet reporter and blogger. Du Ri’s brother, Seong Gyun, visits them. Seong Gyun hates Do Shi, and dislikes that he still did not marry his sister. In room 610: Jeong Yeong Jun and Choi Jin Nyeo, a couple with 12 years gap, started living together 1 year ago after just dating for 2 years. Yeong Jun is a guitars and Jin Nyeo owns a shop that sells side dishes. Room 709: Lee Jun Jae has been living alone for 2 years after his parents were transferred overseas. Currently he is looking for a roommate, and Takuya, a Japanese traveler whose last stop is in Korea, decided to live with him as a roommate for 3 months. Room 510: Park Hwan Jong and Ha Seol Eun, a couple that decided to get married after just 3 months of dating. Seol Eun is getting ready to start a business, Hwan Jong is part-time lecturer.
Room 609: Du Ri thinks Do Shi has a mental issue because he keeps trash in his backpack, however she is just like him and has a ticket for the movie “Titanic”. Later, they fight about the taste of ramen. Du Ri celebrates Do Shi’s birthday. Room 610: Yeong Jun’s sister, Na Yeong, come to visit. Yeong Jun and Jin Nyeo try to hide that they are dating and living together from her, because she has a big mouth. At night, Yeong Jun misunderstands and thinks Jin Nyeo is having sex when he is not there. Room 709: Min Jae, enters the open apartment to deliver a package. However, he hears panting and thinks Jun Jae and Takuya are having sex. Instead, it turns out they are cleaning the bathroom. Takuya enters on Jun Jae when he is watching porn, he then decides to teach Jun Jae Japanese so he can understand what is being said in porn movies. Room 510: Hwan Jong asks Seol Eun to have sex, however he keeps disturbing her while she is in the toilet and she gets angry with him.
Room 609: Do Shi finds Du Ri’s reusable pad and uses it as a towel, without knowing what it is. Do Shi and Du Ri meet Hwan Jong and Seol Eun while removing dust from their bed sheets. Do Shi and Hwan Jong start competing who is the strongest duster. Du Ri asks Do Shi to accompany her to their friend’s wedding, however he refuses because he feels inferior to them. Room 610: Jin Nyeo buys a new short dress, which turns out to be small on her and keeps tempting Yeong Jun. Later, Jin Nyeo uses Facebook to look for her first love. She then sees Yeong Jun’s ex-girlfriend and tries to imitate her. Jin Nyeo comes back home acting drunk to have a serious talk with Yeong Jun, making him feel bad in case he ever tries to leave her. Room 709: Jun Jae tries to kiss Takuya, after Takuya helped him put his tie on. Room 510: Hwan Jong wants to have sex with Seol Eun, but she is uncomfortable about her body hair. She asks him to tie her up so he arm wouldn't move and he wouldn't see her armpits.
Room 609: Du Ri brings over her nephew, Sang Go, and he keeps annoying Do Shi with his questions. Do Shi decides not to sell his car because of their memories. Room 610: While getting ready Jin Nyeo did not have the time and missed up her make up. When Yeong Jun’s bandmates see her, she pretends that it is marks from Yeong Jun assaulting her. Later, Jin Nyeo dreams that Yeong Jun tries to cheat on her when she is gone to her mother’s house. Room 709: Jun Jae doesn't kiss Takuya. Later, Jun Jae keeps farting on Takuya thinking he did not notice. However when Takuya farts on Jun Jae he faints. When trying to perform mouth to mouth, Takuya smells Jun Jae’s breath and faints. Hwan Jong come to take his delivery and think Jun Jae and Takuya are having sex, however they were actually moving the furniture. Room 510: Hwan Jong’s parents comes to visit and Seol Eun tries to look good in front of his mother. Later, Hwan Jong accidently drop all of their condoms on his mother.
Room 609: Do Shi and Du Ri fight about who will take the stuff they bought together in case they ever break up. Du Ri's mother comes to visit suddenly, however she doesn't know about them living together. Do Shi tries to cook for Du Ri. Room 610: Yeong Jun has a wet dream and turns out Jin Nyeo's mother was the one in the dream. Later, Jin Nyeo's mother visits suddenly and finds Yeong Jun. Her mother asks Yeong Jun about marriage but he doesn't reply and she asks Jin Nyeo to break up. Kim Poong comes to visit and Yeong Jun gets competitive with him. Room 709: Jun Jae keeps thinking sexual thoughts about Takuya. Room 510: Hwan Jong tells Seol Eun that she will gain weight from eating junk food.
Room 609: Seong Gyun, Du Ri’s brother, visits and tell them he is getting married to his girlfriend who he dated for 3 month only. He keeps asking them to get married too. Du Ri brings home a lost dog until they find its owner. Du Ri and Do Shi have their friends over. Room 610: Jin Nyeo and Yeong Jun start competing and keep hitting each other. Yeong Jun accidently breaks Jin Nyeo’s teeth. Later, Yeong Jun invites his friends who keep making rude comments about Yeong Jun dating an older woman. Jin Nyeo hears them and is hurt, but Yeong Jun kicks them out. Room 709: Hae Ryung, Takuya’s friend visit and Jun Jae is jealous of her. He calls Min Jae to drink with them. Min Jae keeps hitting on her, and she leaves. Room 510: Edible underwear arrives by mail, and Seol Eun tells Hwan Jong that it is a present from her gay friend from Paris. However, Hwan Jong believe this gay friend was more than a friend when Seol Eun was living in Paris.
Room 609: Do Shi’s ex-girlfriend come to visit and tells Du Ri that Do Shi proposed to her in the past. Both of them fight and Do Shi knocks his ex-girlfriend unconscious. He tells Du Ri that she is the one for him and his ex-girlfriend is not his style anymore. Room 610: Jun Jae helps Jin Nyeo carry a rice bag and she finds him attractive. She later dreams about having sex with him. Yeong Jun finds out about the dream and is mad about it, so he farts on the elevator while Jun Jae was on it. Room 709: Takuya finds out that Jun Jae has a girlfriend. Jun Jae has a date with his girlfriend but he does not want to do and leave Takuya alone. He then bails on his girlfriend and stay with Takuya. Jun Jae finally acknowledges that he like Takuya. Room 510: Hwan Jong parks his car in front of Do Shi’s car. Do Shi keeps calling him to move his car, while Hwan Jong is having sex. When Hwan Jong arrives, Jun Jae try to breaks the fight after Do Shi starts fighting with Hwan Jong.
Room 609: Do Shi tries to take revenge after Du Ri posted a picture of him online and her friends made fun of him. She then post a video of him while on the toilet because he broke a promise with his. Do Shi gets a bad haircut and Du Ri makes fun of him. Du Ri tries to spice there love life because she thinks Do Shi is bored with it. She licks Do Shi’s feet however she gets Athlete Foot fungal Infection from Do Shi’s feet. Room 610: Yeong Jun help Jin Nyeo sort her clothes. Room 709: Takuya has something stuck between his teeth and Jun Jae is afraid of telling him because it might hurt his feelings. Room 510: Seol Eun want to buy a laser hair removal device for Hwan Jong’s birthday. In reality, she wants it for herself and Hwan Jong know but allows her to buy it. He vows to take revenge and buy her engine oil on her birthday.
Room 609: Du Ri and Do Shi buy clothes online and all of it looks bad. Du Ri has bad day were everything she does go wrong. Du Ri is sick but tells Do Shi to go to his reunion. Do Shi comes back early because he is worried about Du RI. Room 610: Jin Nyeo buys unnecessary thing and then hits Yeong Jun for wasting money on buying an expensive electronic drum. She then hit him again when he tells her he bought another game as well. Yeong Jun is angry because she buys unnecessary and he cannot. Jin Nyeo meets Seol Eun, and Seol Eun keeps annoying her with her talk about marriage. They then keep competing against each other and keep bragging. However, their boyfriends' embarrass them. Room 709: Jun Jae tries to avoid Takuya because he thinks that they cannot be together. Room 510: Seol Eun forces Hwan Jong to watch a beauty show with her and then put makeup on him. His makeup turns out horrible.
Room 609: Do Shi and Du Ri silently fight with each other. Du Ri loses her phone and brings her old phone. Do Shi sees a man’s photo and thinks she was dating an older man, but turns out, he is her father. Room 610: Jin Nyeo asks Yeong Jun why he likes her. Jin Nyeo takes a pregnancy test and thinks she is pregnant. She think Yeong Jun is young and is afraid of telling him. She keeps craving strawberries and Yeong Jun later understands. Jin Nyeo go to the doctor but turns out, she is not pregnant. Yeong Jun name become the first in search results because of a funny video and he is offered a role in a matchmaking variety show. Jin Nyeo tells him to go but he refuses. Later, Yeong Jun keeps getting variety show roles. Room 709: Takuya asks Jun Jae if he likes him and why.
Room 609: Du Ri keeps suggesting places to visit but Do Shi wants to stay home. Do Shi thinks about quitting his job as a voice actor. He also thinks he has insomnia because of his job but he later realizes that voice acting is the best job for him. Room 610: Jin Nye tries to create a secret code with Yeong Jun. Yeong Jun then imitates Jin Nye on a radio show as a secret code; however, Jin Nye is embarrassed. Everyone meets in Jin Nyeo’s apartment for an apartment meeting. Jin Nyeo and Seol Eun compete by showing off their bodies in front of their neighbors. The manager is angry because someone throw their condom trash bag in the hallway. Jin Nyeo and Seol Eun later start fighting. Room 709: Jun Jae girlfriend comes to visit suddenly. She thinks he is cheating on her and he tells her he likes someone he cannot date and asks her to break up. Room 510: Hwan Jong tries to impress Seol Eun with his limited movie knowledge after knowing that she finds movie critics sexy.
Room 609: Do Shi fails an employment test but Du Ri passes. Du Ri now goes to work and Do Shi stays alone. Do Shi tells Du Ri he is moving out and is going to stay with his mother for a while because of his father’s health. Du Ri suggests getting married but Do Shi refuse. Do Shi comes back and he moves out with Du Ri. Room 610: Yeong Jun is busy with his career but now Ji Nyeo wants him to be with her. Yeong Jun is forced to move out by his manager but he goes back. Yeong Jun fills the marriage certificate and he tells Jin Nyeo about the new apartment. Yeong Jun and Jin Nyeo have a baby. Room 709: Takuya leaves after learned about Jun Jae’s feelings because he too likes Jun Jae but is afraid. Jun Jae goes to Japan and moves in with Takuya. Room 510: Seol Eun is nervous about the upcoming wedding and think Hwan Jong is different from her and they fight. She asks him if he likes her but he doesn’t answer her. Seol Eun marries a foreigner and Hwan Jong is still alone.