Both are quirky mini dramas with a feel good undertone despite the unfortunate/bad circumstances of how each story came to be.
Both dramas have fantasy world-building that tangents the horror genre. Black focuses mainly on grim reapers while a korean odyssey tries to incorporate/explore many other myths.
Lee Min Ki in both dramas as the main lead! Cannot unsee though that he plays a kind of reversed role in Because this is my first life as opposed to Dalja's spring; while he is the younger guy dating an older woman in the older drama, he is certainly Dalja in This is my first life, what with being an old spinster type of guy, counting his money and being all scrooge-y.
Both dramas are sweet and about two totally different people developing feelings for each other as they learn to depend on the other while living together, although Kimi wa petto is a bit more extreme with the conditions for tenancy ;)
Falling in love after getting married! Goong has a bit more tears and teenage drama while Because this is my first life is a bit more mature but innocent in a way as well, both are focusing mainly on the development of the main couple's relationship. Also, the main actresses look quite similar.
Both dramas have these funny skits at the end/begging of each episode. Delightful girl Choon Hyang has historical skits while the main story is set in modern time and King is not easy has modern skits while having a historical setting for the main story.
About sibling bonds and never giving up, both dramas try to explore the more darker side of the human nature. Circle is heavy on the scifi with an array of never ending plot twists while I remember you has a bit of the more typical crime/mystery flare within the rom-com genre, though with its own fair share of twists and turns.
Both have crime, mystery and a dash of scifi, even though circle is a bit more heavy on the scifi and quite more fast paced. Both dramas are also about people struggling against corrupt/underground organizations planning to make the world a "better" place.
Time travel and romance in both dramas! However, the lead in Nine uses time travel more purposefully to uncover secrets in the past which sometimes makes huge riffles and changes to his present, while Tomorrow seems to be more about traveling to the future and trying to affect it by changing the present. Nine has also a more serious/darker undertone to it.
Both are mini-dramas with the same male leads. One is about a new love with some fantasy elements while the other one is exploring what happens after the love ends.
Both movies are real tearjerkers! Cute tho. My Bromance is obviously BL.