Love is Sweet and My Little Happiness are very similar on the terms of a strong independent female lead and a wealth male lead. They also both have history with each other back when they were little kids..

Killer and Healer has a very similar vibe to S.C.I. Mystery. The two main characters have a yin and yang type relationship. Good and evil, but able to get along to the point that they work well together.
They both have one character that is a cop while the other is in a different field. The bromance is strong in both dramas.

In both The Sword and The Brocade and General's Lady the two main leads are put into a 'forced" arrange marriage. They both give a similar story vibe.

They are basically about a teacher that is in charge of a class that has no discipline. the teacher is able to connect and help out in the students lives and motivate them to study and think of their future.
a plus both teachers are really good fighters and end up getting into fights, which gives it some interesting content to follow.

Both dramas are of an alien that arrives on earth and falls in love. In My Girlfriend is an Alien the FML is looking for something she lost while in Falling in Love with Cats the FML is looking for the one that saved her all those years ago.

Both FML are able to see ghosts, while the ML is the one responsible of catching the ghosts.
In Devils Punisher the ML is the Ghost kings, while in Black the ML is a Grim Reaper.

The Mystic Nine is the prequel of the The Lost Tomb series. The time period is 50 years before the main event, so all the characters are different.

The Lost Tomb 2 is the Prequel of Reunion: The Sound of the Providence Season 2. It is also the sequel of The Lost Tomb which is the parent story The sound of the Providence.
The characters are the same, but not the actors.

The Lost Tomb is the prequel of Reunion: The Sound of the Providence Season 2. It contains the same characters, but with different actors.

Reunion: The Sound of the Providence is the first season of Reunion: The Sound of the Providence following were season 1 left of at and continuing with the same actors.

It's also related the solving cases with one of the male leads being overly smarter then an normal detective. The bromance between the two male character are similar, but I think for S.C.I. they toned it down.