The stories are vastly different but I couldn't help but notice similarities between both dramas.
Similarities:
-The main female leads look and dress alike.
-The female leads are curious about the world but also shy (Heart to Heart's character has an actual social phobia and is WAY worse)
-The female leads knit and have a cleaning obsession.
-The romance between the male and female lead is VERY unusual and the people around them are always trying to break things off. (For the sake of the female lead)
Differences:
- Plot: Heart to Heart centers around a woman who has severe social phobia and slowly develops a relationship with her psychiatrist. Mary Stayed Out All Night is about a girl who's desperately trying to get out of an arrange marriage and gets into a fake marriage with a stranger she hits with her car...
- Romance:The psychiatrist falls and chases after the female lead first in Heart to Heart but Mary Stayed Out All Night is the other way around.
-Heart To Heart centers around the psychiatrist's job and the people they meet along the way whereas Mary Stayed Out All Night is focused on music and whether the female lead will escape the arrange marriage or not.
Both shows have a lot of charm to them and is great for a rainy day!!

Similarities:
-The female leads are played by the same actress in both 3 Nen a Gumi and Mask Ward
-Both stories are centered around a hostage situation gone wrong.
-Both stories have a theme of revenge and justice.
-Both deal with controversial topics
Differences:
-3 Nen a Gumi takes place in a classroom, and Mask Ward takes place in a mental institution/nursing home.
- 3 Nen a Gumi is about the suicide of a classmate meanwhile Mask Ward deals with corruption inside the institution.
- 3 Nen A Gumi deals with the corruption in society whereas Mask Ward deals with political and medical corruption.
I recommend both the drama and film if you enjoy a good mystery and psychological thriller.