Recommendations

They are both very similar, both have similar female characters which they are best friends and they always go out for food, talk about love stories, and their friendship is built to be more and more powerful...

Though one is korean and another is Chinese these dramas have a lot of overlap.
Both are medical dramas with the MLs having a mentorship type of relationship growing into romance.

it's the same set but different actors and actresses with more disgusting characters and events.
if you liked sky castle you will most definitely like penthouse. it even has a s2 and s3 now lmao.

The four characters are individually contrasting in both the dramas
RUN-ON starts by describing how it dovetails four antique characters-Loser,Psycho,Trash and Crazy . Trot has four leads as well with pretty similar characterizations. If you like SeoDanHa from Runon you'll like the counterpart as well.
Both are not over dramatized with witty and reasonably realistic dialogues.

Both movies portray life segments of melancholic, lonely and thirsty for love cops and have the same artistic and intriguing noir vibes, with stunning neon-textured cinematography and magnificent night shoots across city streets.

-They are both crazy shows
-ML is obsessed with the FL
-ML is basically a stacker too
-Both are interesting shows that no matter how crazy they are you can't stop watching it

Both have powers this might be the only common thing but if you like this I think u will definitely like that too.

Both are centered around women, Search: WWW consist of 3 female leads who hate each other but started to become friends just like how Age of Youth girlies couldn’t recognize each other than began to be besties.

It's most similar in the play of psychological thriller sense. Although Cello is caught up between supernatural and psychological, Insane also gave that thrills and chills with it's great execution of the plot.

For me Insane is most similar to the kind of movie I imagined Cello to deliver.

Double Mints is a darker take on the BL mafia genre and master/servant mechanics that we will see on Kinn Porsche

Both series feature mafia/hitmans as their main characthers. Chasing scenes and all the mafia style seduction is similar.

Both series have a mafia heir as their main characther seducing an outsider and the trailer have some look alike scenes.

We Best Love: No. 1 for You features swimming as a sport and so is Water Boyy. Both series also have BL elements of a drama. Both of them also feature cute main characters in a school setting.

In both the series they live together. In the beginning they don’t like eachother and in the end they love eachother.

They also try to fight hardships with their restaurant or pub, and the vibe was similar.
I know the cast in this is more young, inexperienced and this one seemed less mature, it could be great for those who are searching for something similar.

The relationship is from hate to love and the friendship is great as well. Although it can't beat Itaewon class for me, it is similar in many ways, has a nice ost as well and I think the actors did a good job. This one is more relaxing :)