Prequel to New Sexy Simpleton

Bishie boy that got transferred and visited Ohn Noori, Lee Sun-Uh. I was surely suprised that my father, who I never met myself, had sent him, but to say he's one of my fiancé candidates! AND WHAT?My father is the king of a secret kingdom?Oh my~Then I... am a princess? With two fiance candidates, I ended up with a happy headache...Ahhhh~Who should I pick to make the right choice?

The countdown of the human species began.The sun has come closer to Earth, causing radioactive rays that kill all female fetus. Some mothers even died during their daughter's miscarriage due to hemorrhage.Confusion reigned homo sapiens' first phase of extinction: mate competition, countries vying for a solution, families losing their loved ones. The government has required all females to take tests to collect data for research on developing a cure. Ho Su was identified as the one who is immune to the radioactive rays emitting from the sun. To prevent war between nations over her, Professor Yun has kept his founding about her immune a secret and has persuaded Ho Su's father to let him freeze Ho Su in hibernation, waiting for a time when the situation has stabilized from chaos to experiment on her for a vaccine.

From HMR:
This is the sequel series to Sexy Simpleton, but don't worry you won't be lost! Eun Bi, the popular CF model, is back in modern times with her ancient Korean boyfriend. Yet the adventure's not over yet, as she's transported back into ancient Korea. Will she manage to find the shoes that can bring her back?

Power, body, charisma all together it shakes the mind. Provoked the gym teacher to seduce his nervous mind. The first kiss then, second kiss to seduce. Who is really the person that makes Chunja's heart thump? That person is...!!...
(Source: Fateful Encounters)

From Hwang Mi Ri's Palace:
After losing her entire family to a mysterious fire, Soon-Doong refuses to wallow in sadness and decides to move to South Korea from her native Yanbian to find herself a new and better life. Holding nothing but a plane ticket to Korea, a small package of clothes, and a half-burnt letter between her grandfather and a "textile factory owner" in Seoul (who were good friends), she resolves to find a job at the factory and make a decent, honest living. Only, the "textile factory owner" just happens to be the CEO of the biggest clothing brand in the country, and her grandfather wasn't just a good friend with the "textile factory owner" - he had saved the CEO's life and lent him the money to start the business that he has today! And so begins Soon-Doong's life in Korea, as she shatters everyone's bigoted prejudice against ethnic Koreans who came from Yanbian and makes everyone rethink about their own values and lifestyles.

From [ RC-SCANS ]:
Gook Eun-Song is your average high school girl... that is until her attractive younger sister steals the man she had a crush on. Depressed, Eun-Song purchased a bottle of alcohol and crawled into a supposedly cursed closet in her father's furniture store. Yu Ha is your average typical bad boy. He even broke traffic regulations just to end up being chased by a couple of police officers.
Oddly enough, he also ended up in the same closet where Eun-Song is asleep from drinking too much. Yu Ha ends up sleeping in the cursed closet with Eun-Song by his side... just to find out the next day, their bodies have been *gasp* switched!
Can anything else possibly go wrong for our poor heroine?

Boy-crazy Jae Yoo is willing to go through any underhanded means if it means living in the boarding house full of hot guys… Even if it’s going out on a blind date with the dorkiest boy in the school. When she dumps the guy immediately after, she pisses off his handsome best friend Ji Hu and from that point on, the two are constantly going at each other’s throats like cats and dogs. When Jae Yoo finally accomplishes her dream of entering the “boarding house of hunks,” she thinks that nothing could go wrong. An amazing house, a kind landlady, and even a cute guy who seems to be interested in her… What’s this?! Ji Hu is the landlady’s son?! And how is it that he knows about Jae Yoo’s most embarrassing moment in life? What kind of life will the two lead under the same roof? Will they be able to live together at all?!

-
Summary from another:

Using all sneaky means possible, Jae Yoo has broken through the harsh competition and gotten herself into the boarding house full of hotties.

However, she is on bad terms with the resident # 1 hunk Ji Hu...

"Bastard, a good looking face doesn't make a hunk! A hunk should act like a hunk to be one!"

Will commoner Jae Yoo make the quality of the boarding house better? Or will she make it worse? That's up to Ji Hu.

When a tough, lazy, money loving, yet beautiful high school student named Shin Bia jumps down from a building , she thought she would die but instead she falls into the era where the ancient Goryeo Dynasty ruled?! She had to transform into a proper and elegant lady and while she's there she faces many obstacles.

From Saigo no Shou Scanlation:
Hu Reum no longer has a family, and so now must go live with her cousins. Will she find her first love? Will she let barriers stand between it? So far, a pretty funny story with an ensemble of four guys (ranging in personalities) and the girl, Hu Reum.
Do not confuse this with the series 'I want you'.

It all starts when she was 8. He was kind, and nice to her.
Yeo Jin is now 17 years old, and she moved back from Busan to Seoul to meet her first love... but when she arrives he has completely changed...
(Source: little sheep scans)

'S' is a known as a bully caretaker, who avenges her bullied clients -- for a price, of course.

However, in reality, 'S' is a nerd named Kang Song Ih, with a twin brother named Kang Ah Eul, whom she loves above anything. Ah Eul attends Chungha High School, a famous and expensive school, but over winter break, he attempts to commit suicide. Song Ih, determined to understand why her brother tried to kill himself, attends Chungha High School, pretending to be Ah Eul -- uncovering the reasons why Ah Eul was driven to suicide, including one mysteriously handsome but "bad" guy named Seo Ga Yoon.

Read as you follow her life while staying in an All-Boy's school and living in a dorm -- with a male roommate, who happens to be a famous singer and someone she as "S" had once nearly beat up.

Watch out! Whoever bothers "S"'s brother, prepare to face her!