A man and a woman are brought together because of their spouses' indiscretions.

Both movies show the main protagonists experimenting the first flutters of love...

Historical dramas centered on a woman (empress).

Empress Ki takes place in Korea while The Empress of China takes place in China.

Both dramas have 2 strong parallel leads whose characterizations are really well done.

Both are also noir/crime drama.

In both the movies, the husband is scheming behind his wife's back.

Both movies have a taciturn lead whose armor gets stripped down by the girl.
Both movies are the story of two jaded people falling in love...

Though Cyrano Agency leans more on the romantic comedy side and Architecture 101 on the melodrama one, both deal with the bittersweetness of first love.

Both dramas deal with a couple getting married because of an arrangement and because the girl is head over heels for the guy. Though Wedding is more mature than than Sweet 18.