Because This Is My First Life (2017)

the vibe is similar because the story discuss about what truly happened in society when women don't get married

These dramas are both innocent cohabitation stories, and it's very focused on the main characters and their feelings, which was the best part in my opinion. I often dislike it when dramas try to cram so much into the story that they neglect to develop the main story, the reason why people watch in the first place. There's lots of cute moments in both stories, but they're realistic and not diabetes inducing or forced. I highly recommend them both, and if you liked one, I'm sure you'll like the other! :))

Even though Nam Se-hee Is not mentioned as an autistic person, he shares some characteristics that could indicate that he's in the spectrum. For example, he is very inflexible regarding routine changes, he likes order and cleanliness (it can't be said that these characteristics are specifically of those in the spectrum, but in this case it can be considered as such), among many other things.
The more you know Nam Se-hee, you start to realize that he's autistic.
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Aunque Nam Se-hee no se menciona como una persona autista, comparte algunas características que podrían indicar que está en el espectro. Por ejemplo, es una persona de mente cuadrada con relación a su rutina, le gusta el orden y la limpieza (no podemos decir que estás características sean especialmente del aspecto, pero en este caso podríamos considerarlo), entre muchas otras cosas.
Cuanto más conoces a Nam Se-hee, empiezas a darte cuenta de que tiene mucho de autista.

In both dramas two unrelated people starts to live together without any feelings, but later on they learn to care for each other and become inseperatable.

Both shows revolve around a group of close friends who are in the workforce for a number of years. While BTIMFL has more romance, both dramas show workplace struggles and explores concerns about settling down.

There's also a quote from BTIMFL that always comes to my mind while watching ROTP: "Seoul is too cold."

Somehow they both give off a similar vibe. I feel that the humour (I laughed so hard in SWDBS and am finally finding something that makes me laugh just as much with BTIMFL) and the mix of lighthearted romance with pretty serious elements are kind of similar.
The storyline and the characters are totally different though. Although they are kind of the only progressive k-dramas out there: strong female leads and challenge of traditions.

Not the same plot. Not exactly the same theme. But both talk about marriage in mature tone. Both has beautiful dialogues, scenes, writing and directing. And as a plus, this has great sceneries to boast. Indeed a well-produced drama.

They have the same realistic but comedic feeling. Both deal with the struggles of korean youth/young adults and the main male leads are anti-social.

If you want to watch sometning abouut contract marriage then you can try with this drama. Prime Minister is a cold person who has to take a mariage because someone took the photo them and wrote in whole magazines about Prime Minister's lover.

I think both of these have many similar concepts. In both of these dramas, there is a couple having trouble in their long relationship. There is also also a similarity in the concept of “dreams” too.

Both focuses on women 30+ finding love but the biggest similarity is the close female friendships and how they all experience different loves and relationship challenges.

Both showcase healthy relationships between the leads and deal with their emotions in a very subtle and sensitive manner. They are both rooted in reality and deal with prevalent issues without being preachy or boring. It's definitely refreshing to see male leads respecting their partners and giving them their space. They are both slow romances, Radiant office more so but that's part of what makes it so gratifying at the end. They are not your typical K dramas and are hence grossly underrated. They are not for everyone but they're definitely worth your time.

While the overall story lines of 20th Century Boy and Girl and Because This is My First Life are fairly different, the way the stories are presented are quite similar. They shows split the screen time between couples and occasionally pull them back together for shared scenes. Also both shows have a wholesome light feeling throughout!

Both “She and Her Perfect Husband” and “Because This Is My First Life” plot’s purpose is on contract marraige

Yae, an unremarkable girl working in a café and living with a friend, finds herself unable to afford rent when her friend suddenly gets married, and she loses her job in the same day! It’s only when her boyfriend dumps her that she finally hits rock bottom. She’s at her wits’ end when her childhood friend Takumi suddenly reappears into her life. Takumi suggests that Yae take on a part-time job as his “fake wife” for the next six months. He has his reasons for wanting people to think he’s married. Yae has no other choice but to accept his proposal, and in return receives housing and living expenses for playing the role of his “fake wife.” So begins a “fake marriage” with a time limit. Unbeknownst to Yae, she was Takumi’s first love, even though she thinks of him as nothing more than a childhood friend. Takumi struggles awkwardly but earnestly to win Yae’s heart and find true love. Even though their marriage starts as a sham, will the day come when this couple can become something more?