emeraldarrows

Very different in plot and tone but both have mermen prince MLs who are a bit innocent at the beginning of the dramas.

Both are short length dramas about a merman ML and a human FL who end up living together. The ML is very naïve about the human world and requires the FL's help to obtain something so he can return to the ocean.

Both dramas are a mix of crime/mystery and legal genres involving a serial killer. Determining who is guilty and innocent is difficult at the beginning, with many twists in the plot. Both dramas have a similar tone/feel.

One is the original series, the other a bonus epilogue that adds a bit more and has a happy ending as well.

One is the original drama, the other is some extended scenes.
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Both FLs are self-aware and supporting characters determined to change their fate within the world of a novel or manga. The ML also becomes self-aware and work together to change the story. In both dramas the characters are controlled by the author against their will during a scene, but off-scene are free to act as they wish.

Both are dark mystery/crime dramas with a group of detectives trying to identify a sadistic serial killer. The same actor is the ML in both.

Both dramas have a dark and creepy vibe and are about a serial killer connected to the past and present. Both MLs seem to have a dark side/are believed to have a dark side.

Both are short length Korean dramas in which someone gets a chance to return to the past and attempt to save someone they cared about who died tragically back then.

Both are short length dramas in which someone returns to the past and tries to save the life of someone who died back then.

Both are short length Korean dramas in which someone gets a chance to return to the past and attempt to save someone they cared about who died tragically back then.

One is a BL and the other M/F, but both are about someone getting a chance to travel to the past and hopefully save someone who died back then. Neither relationship was romantic in the current timeline (in SFOT she barely noticed him and in OA he viewed him as a big brother) but becomes romantic when the person travels to the past. Both dramas have a similar sort of melancholy vibe.