Marriage contract

https://mydramalist.com/210-my-little-bride - movie, very similar plot to Sweet 18

https://mydramalist.com/18774-something-about-1-percent - I love the chemistry of the leads in this one

https://mydramalist.com/16311-marriage-contract - this one's a melodrama though, but it is beautifully made 

https://mydramalist.com/27647-bride-for-rent - Filipino romcom movie

This si actually one of my favorite troupes, I wrote an article about this here: https://mydramalist.com/article/2016/08/23/top-10-dramas-with-contracted-relationships

Contract marriage:

• https://mydramalist.com/19702-nigeru-wa-haji-da-ga-yaku-ni-tatsu
• https://mydramalist.com/16311-marriage-contract
• https://mydramalist.com/142-delightful-girl-choon-hyang
• https://mydramalist.com/9558-fated-to-love-you  (korean)
• https://mydramalist.com/747-fated-to-love-you (taiwanese)
• https://mydramalist.com/38-goong
• https://mydramalist.com/275-nagareboshi
• https://mydramalist.com/13388-mask
• https://mydramalist.com/21-mary-stayed-out-all-night
• https://mydramalist.com/760-sunny-happiness
• https://mydramalist.com/24-full-house-
• https://mydramalist.com/371-that-fool
• https://mydramalist.com/321-wonderful-life-2005
• https://mydramalist.com/24678-because-this-is-my-first-life
• https://mydramalist.com/18550-hapimari-happy-marriage
• https://mydramalist.com/15792-best-lover

Contract relationship

• https://mydramalist.com/491-pride
• https://mydramalist.com/18774-something-about-1-percent (later they get married)
• https://mydramalist.com/198-1-of-anything (later they get married)
• https://mydramalist.com/106-smiling-pasta
• https://mydramalist.com/199-creating-destiny (later they get married)

https://www.youtube.com/watch?v=oAK3-xHANv0