Train (2020)

Yoon Shi Yoon, aka the master of double roles. In Train he plays 2 versions of the same detective with different personalities living in different worlds, while in Psychopath Diary, he plays the role of a timid office worker who believes he is a serial killer and has small bursts of moments where he "becomes" one.

Both shows also revolve around trying to find a serial killer. In Train the story focuses on finding who the killer is, while in Psychopath Diary the story reveals the killer in the first episode.

Psychopath Diary is more a comedic dark mystery, with moments that will make you laugh, while Train is more of a typical strict crime show. Both shows include crumbs of romance, but it is not the overarching focus.

Although the story lines aren’t similar, the concept of transportation system (a train in Train and the subway in Catch the Ghost) is what the mystery in both dramas are based on. The killers in both dramas have a similar strategy in murders too, both having to do with suitcases...

The tone of the drama is similar. Few words are repeatedly used by the main leads in all the episodes. Both dramas doesn't proceed in the way you expect it to be.

gripping, complex & full of dark and futuristic themes, both of these dramas are absolute must-watches, particularly if you want to watch something special & unlike many other dramas
>> the execution of the dimension-switching in train is highly convincing, plus very reminiscent of the divided timelines in circle
>> similar overall vibes (although train is more supernatural? vs circle's scifi)
>> both focus heavily on investigations
>> the male leads suffer traumatic losses, dedicate their lives to protecting their loved ones & uncover some nasty truths along the way
>> ...with a side of thought-provoking (and often mind-blowing) moral/ethical issues caused by messing with fate (train) and memories (circle), and how these can butterfly effect to drastic proportions.

The scene that appears at the beginning of the series is similar. Those trying to convey the drama look alike. Even if they are of different types. But also different lives and choices, and the events that result from them are very similar.

- doppelganger identity switch as both are from time travel and the good/evil impersonate like the other one
- plenty of twists, thriller & every episode will keep you on the edge of what happens next