Orange Marmalade and Blood are both vampire dramas.
In Orange Marmalade (it didn't air yet), if they follow the webtoon, it should be about a female vampire in high school falling in love with a boy who hates vampires.
In Blood, the vampire is a surgeon looking for a way to become human and trying to figure out who killed his parents.

In both drama, a rich boy gets a girl pregnant by mistaking her for someone else, then fall in love with her.

Both dramas are romances about female bodyguards... Although there isn't much action in Sweet Sweet Bodyguards, it's still enjoyable ^^

Both dramas are about a male student falling madly in love with a female teacher.
Romance is more on the taboo side about teacher x student relashionship while Biscuit Teacher and Star Candy is more about the romantic feeling of the young student.
Side stories also preventing them to be together :
- Romance : the woman's family is responsible for the boy's father suicide.
- BT&SC : the teacher is romantically involved with a co-worker, who happens to be the boy's uncle.

Nearly the same story-line. Both time-travel dramas where the heroe has to either adapt himself to ancient times or/and keep the history on the right path.