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Both protagonists are two high school students. In Splash Splash LOVE, the female protagonist arrives in the Joseon Kingdom thanks to a puddle. In Tinted with You the male protagonist arrives in a feudal era by means of a painting. They will both meet a crown prince and fall in love.

Both movies are about long distance sport.
One is speed walking, the other is marathon running.
Both are tough sport. Need perseverance, determination

In both dramas three best friends, Each pursue different paths in both career and love. Despite life's difficulties, the three friends can always return home at the end of the day and support each other.

So I am surprised nobody added these two yet because they are very similar.
Girls and Guys are stuck in one place together as they have to build relationships, get some kind of missions to help them interact.
Both have people watching it and commenting the actions which makes it even more entertaining.
As I waited for Single's Inferno new eps I discovered this and it was great to point I went back on Love Catcher 1st season too because 3rd is still airing.
However I think 3rd season is more alike to Single's Inferno maybe because it has similar vibes since they both are airing on 2021

Both involve a good coach leave the city and went to rural area. Form a team from scratch.
Many under privilege and young men/boys.
Many hardship, full of talent
Both movie involved international competition

Both movies involve unique sport with the gold to win the international game or competition.
Many hardship, obstacle and many practice.
They represent their country with pride

Both female leads find themselves in a difficult situation until they meet a man that will supposedly save them. They find themselves in situations where they end up faking their love (DAYS - so that he will die) (CLOY - So that she doesn't die or get caught as a South Korean). Through this, they both bicker quite a bit but eventually gain feelings for each other. Although they start to like each other, they both do not realise. The male leads have both made the promise to keep her safe but when she sacrifices herself, they become quite frustrated and realise they may have feelings.

Both sport movies involve put together a group of young men with the gold to win the Olympic.
Many challenges and issues.
Can they make it? Can they win?

Both movie involve the sport with the goal to win the Olympic.
Both movie the team were put together from scratch.
Many challenges, with faith, encouragement, hard practice, and team work, can it happen?

Unique sport with touch of romance.
One is row boat, the other one is ballet.
To success, all the sport need need tough practice.
All sportsmen have to overcome many obstacle, they nee support and encouragement.

A unique sport movie with a touch of romance
Hard practice. Love blossom.
Beautiful couple. Sport with grace. Mutual understanding

friend group from high school to work-life
"stupid" girl goes after the most popular boy in school
fluff

Both dramas are about being young and having dreams, when all life seem to be still in front. However, in GBC it is also shown, that not all dreams can come true and your life can turn out completely different than you imagined.
GBC and EW both have similar kind of humour, but also include touching and sad moments.
Also, if you liked Lee Joon Ki in Eulachacha Waikiki, in GBC there is a very similar character played by the same actor, Lee Yi Kyung.
GBC is more about family, while EW is more about friendship, but in general they have a similar feel to them.

Now, before I start, I do want to say that they are completely different stories. Saikou no Rikon focuses on the aftermath of a divorce and Chugakusei Nikki is about a teacher-student relationship over time.

The similarities I found with them is that they both made me so frustrated to the point I wanted to throw myself out a window. With both dramas, the love in the love triangle is so strong that you don't know who's going to get picked or what's going to happen. It leaves you with so much suspense.

They also both have characters (in my opinion) that you can't help but hate because they end up speaking the awful truth (Haraguchi Ritsu (CN) and Uehara Akari (SNR)). They are also technically "the other woman" so their presence may be irritating at times.

Although it’s Korean and not a BL, they are both very interesting. Not Me has not finished yet but I feel like it’s going to be somewhat similar.. They both have to act as someone else to uncover the truth and get justice for the person who is close to them. I hope you can check out My Name. :DDD