Both movies span from high school to adulthood. Male lead who isn't good at his academics decides to buck up because of the female lead. Become unlikely friends and falls in love with each other. Ultimately the leads drift apart due to a quarrel and reunite bcos the female lead is getting married. Some mistakes are irreversible, some words said can never be taken back. Regret lingers heavily at the end of both movies.

Male lead has superpowers from being a subject of experiment as a child, suffers from side effects and is hunted by the scientists as he is their most 'successful' product. Female lead is a cop that helps the male lead. Child actor used for both male leads are the same actor

Both leads were kidnapped together when they were kids, and suffer some sort of trauma/memory loss from it. Male lead has estranged relationship with his brother because of the kidnapping.

Both movies span from junior high/high school till they're adults. Ultimately the leads drift apart due to a quarrel and reunite bcos the female lead is getting married.

Both of these show have the same writer, and is about a writer/artist who enters her own work. The second lead of the work ends up being the first lead of the drama

Both leads have a strained relationship with their mother who raised them alone, and they get teleported back in time when their moms were young. They integrate into the social circle of their mom and her friends, forging a strong friendship while getting to know the young self of their moms better

Both involves a husband who travels to a different dimension where the alternative reality is that they're no longer married to their wife. They both learn how to treasure their wife only after losing her

Both male leads meet their future self and rushes against time to save the female lead lead from her impending death in the present.

Both dramas deal with a single parent raising a son, while the other had no clue about the kid's existence. In AC, it's a single mom but in TKFH it's a single dad. Somehow the parent that left crosses path with the kid, spent time bonding with him and grew fond of him. When they found out the kid was theirs, they go through a custody battle.

Both dramas involve the male lead getting a heart transplant surgery, and ends up falling for the fiancee of his donor. This leads to their personalities changing for the better as well.

Both ghosts investigate the mystery of why they're a ghost. Both villains were evil spirits while putting on an angelic facade. Both dramas were from TVN and while the plot was wildly similar, the casts displayed different chemistry.

Both couples get married while drunk and eventually fall in love