They're both about traumatic pasts and its effect on the main characters. They're both dark and psychologically complex! (love them both)
They both have very intelligent main characters with strategic minds who fight for what they believe to be correct. Both dramas are very well written, keeping the audience engaged from beginning to end.
Both are mystery, crime dramas with extremely well written plots.
Both dramas are noona romance and the chemistry between the leads in both cases is simply breathtaking!