it's the prequel of this drama as it tells a story of one family from the same era and the same composition of the story
they are technically connected plot wise
both have martial arts too in the same era

Both dramas have corrupt cops or seem to be corrupt and a lot of detective work involves drug gangs and very complicated relationships between the cops

Both dramas are drug related police dramas
who involves an undercover cop and a lot of thrilling events

Both dramas are detective dramas who involved two odds of personalities but good friends after they get to know each other

Bromance detective drama and undercover cop
both dramas have that in common
both dramas are really exciting police dramas

It's the second season of the same drama with the same cast but not the same female lead
detective drama

Two drama has similar plot lines
the male lead getting into a trap and get prison time for something he didn't do
trying to escape and prove his innocence is the goal in both dramas

The male leads in both dramas are trained military officers
the male leads in both dramas get tortured for information by the bad guys
both dramas have detective work and loved ones to care for and protect

The male leads in both dramas have daughters trying the protect
the male leads are involved in criminal detective work and trying to do the right thing by their loved ones
the male leads are good at fights

Both bromance movies
Both are about two male friends protecting each other and having amazing friendship

Same male lead in both
same republican era in both
same fighting by smartness in both
they have amazing bromance ,,male friendship
also have good romantic stories not heavy on the romance

They are based on each other as part one and part two
same two male lead in both
same republican era