Pain (2011)

Both male leads are willing to get hurt or die in order to protect and save the female lead.
Both have female leads that can be cured but that causes more problem for the male leads.
Both are sweet, sad and romantic.

Both movies show a raw beauty of a growing relationship between a man and a woman that have many differences but still fit somehow fit perfectly with each-other.

The whole story structure are much similar. Both struggling main lead, heroine is trying to live in the right way and the hero is doing the brute work and getting used by others. Meet , help and fall in love. There's no mention of age gap though.

Similarities-
-Mr. Gu and Kim Ji Won have a similar romantic dynamic as Nam Soon and Dong Hyeon. Both are opposites yet are very sweet to one another.
- *mini-spoiler* Mr. Gu and Nam Soon is a gangster/land-shark
-Both stories are about showing the slow and mundane parts of life
Differences-
-My Liberation Notes is focused on the Jung family, whereas, Pain is about Nam Soon and Dong Hyeon becoming a family with each-other.
-Dong Hyeon is sickly whereas the sisters in My Liberation Notes are healthy.
-Pain is much more of a romance than My Liberation Notes
-Dong Hyeon is much more extroverted than Kim Ji Won
I honestly think anyone who likes Liberation Notes would really enjoy Pain, and vise versa.

In both movies I could see lot of similarities such as both movies deal with bittersweet love story. Male lead trying to protect Female lead.Female lead is homeless.Male Lead and Female Lead staying at same place.Male lead involved in illegal activites