These are all fluffy, light, romance, comedy, with fake marriage / contract marriage as a theme.
Sweet 18
This is actually an arranged marriage. Very fluffy and funny, and lovely.
The FL is still in highschool at the start of series, so some scenes take place in highschool, but after a few episodes she has graduated and there aren't many scenes like that.
But the actress did an awesome job, one of the most memorable characters in such a drama. She is very lively, funny and lovely.
Lie to Me
I really liked this series. A crazy woman lies that she's married to a rich guy, and that little white lie spreads like a wildfire resulting in everybody knowing that they are now married. So because of reasons... they have to act like it.
Marriage, Not Dating
Really enjoyable series about a woman that has given up on dating, and a guy that doesn't want to date, they agree together to enter a contractual fake marriage just to get everybody off their backs. Hilarity ensues.