There is a one night stand that happens by accident which starts a series of events that eventually develops into a relationship between the two main leads.

Similiar both have a one night stand that result in a pregnancy that then develops into a relationship between the two leads. There are trials to go through before they finally get together.

They both have the reincarnation element.
They both are a love story.
They both have a problem to solve.

They both have the reincarnation element. They are a love story but they are different from each other.

They are both about time travel and reincarnation. THe male leads meet the reincarnated versions of ppeople they carre about.

They are both about time travel. IN PN it is a female lead that goes back in time. In IFYLITA it is a male lead that goes back into the past. Both are excellent series.

They are both about time travel . The main leads travel to the past. I think they are pretty close to the same time era.

Both are about time travel. In MQ he falls into a swimming pool and is transported back into the past and switches bodies with a Queen that had tried to drown herself. I thought it was a great series.
In IFYLITA-the male lead gets in a car accident and falls into the river. He wakes up in 1920's.

In both series that have people from the past come to the future.
In LUTYN it is an acupuncturist fronm the past that comes to the future and meets a modern doctor,
In DA it is two women from the past that comes to modern day.

In both dramas they have people from the past coming to the future.
In RF it is the prince and his bodyguards that come forward in time.
In DA it is two women that come from the Joseon era into the future.

Both have a person that is sick and may die that leads to the female and male leads jumping into a relationship.
In SMH- The male lead's mother is diagnosed with cancer and is worried about her son being alone after she dies. So her son jumps into a marriage after only meeting his bride to be one time. The female lead caught her boyfriend cheating on her and decided she wanted to be married to just someone because she wants to escape her parents house and her current life. She meets the male lead through a dating app and they decide to marry without knowing each other.

In GF- the male lead has a brain tumor and is terminal without doing a risky surgery that could result in his death, So he comes to Japan to do some things before he dies. One of those things is he wants to fall in love one last time. He decides to look for someone he can have an affair with so when he dies the girl wouldn't be alone she'd have her husband to support her, He meets the female lead on vacation who is single but she lies and says she married. thus the affair begins. The female lead is attracted to the male lead but she lies about her status because she has tried unsuccessfully to date for years and has been told she is boring ,so on a whim she says she's married.s

Both female leads jump into a relationship with a man they don't know.
In U-the female lead is homeless, jobless and just broke up with her boyfriend,when she is offered to pretend to be married for 6 months tothe male lead. The male lead is secretly in love with her.
In GF- the female lead wants to be married and is instantly attracted to the male lead who she meets on vacation. She lies and says she is married and the male lead says ok let's have an affair.