Recommendations

Both are dramas of a same genre. Both features very cruel and visual crimes. In both dramas you have a specialized team for those crimes. In both dramas some of the main characters have lost their friend or family in a cruel crime. Both dramas also has really good OST and interesting characters.

Both shows are airing at the same time and competing against each other. Meanwhile MixNine is mostly letting the world know about trainees from smaller companies The Unit is about idol group members who have already debuted but failed. There will be idol groups debuting at the end of both shows.

They have a very similar feel to them (e.g. dreamy, fantasy aesthetic). Main leads are connected by some kind of "fate", and they are capable of changing the future a little. If you liked Goblin, you might like While You Were Sleeping. Also, both dramas can be a bit slow (Goblin is slower in my opinion.)

The main couples in both dramas are pretending to be in a relationship to please their families only to fall for each other in the end.

The leads both possess a hidden personality, covering a goofy front with a passion for education. Both dramas deal with the school setting, bad teachers, bullying, and family drama. Both leads are eccentric, charismatic men with a penchant for taking unpredictable actions. If you liked GTO, I highly recommend Kazoku Game.

The plot is almost identical. Both are about strangers getting married due to the benefits rather than love.

The thing that really sets them apart though is that japanese drama is very different from korean. So what you will expect from Nigeru is "child-friendly" while BTMFL is appropriate for a bit older audience.

Just different adaptations of the same famous wuxia novel by Jin Yong (Louis Cha); everyone has their personal favorite version(s). You can really choose any of them, but know this is the first part of the Condor Trilogy and is followed by The Return of the Condor Heroes; that latter is a different story. The third is Heaven Sword and Dragon Saber.

Both are fast pace. They have good story-telling that's why you won't be feeling bored watching it. Both story is about politics and crime... I highly recommend Inside Men if you like these type of movies.

Both protagonists have "supernatural powers" that help protect the other main protagonist in some way. In TY, the male protagonist can see into the future tries to keep close and protect the main female protagonist from her foreseen death. In SWDBS, the female main protagonist has super strength and becomes the male protagonist's bodyguard. Both have very intriging story lines and are highly recommended.

Both films have a similar context but different reasons for killing. In Confessions the teacher performs acts of revenge towards students as she suspects that some may have killed her daughter. Whilst in Lessons of Evil, he kills students for his own sake.

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.

Sunny and Girls' Generation 1979 are both set around similar time periods and both focus on the difficulties of friendship and love as a teenager. Both movies deal with the topics of unrequited love and overall have similar vibes. The first seen of Girls' Generation 1979 really reminded me of Sunny that's why I recommend it. Either way, just watch it, you won't regret it.

Though the story are quite different it really sends off similar vibes and brings up similar topics : women empowerement, sweet & classy revenge, women's friendships, women's social issues (in work...). ASC seems to be slightly better executed, tho ~

They are both quite humorous, though Let's shake it is more over the top (not complaining though ;) Both are historical with a magical/fantastical twist. In general they have a very similar feel.

Both feature the psychological aspect of solving and commiting crimes.
Both main antagonists are seriel killer.
The story and plot are really different though, so it's still refreshing to watch :)