Both have the same vibes.
They have supernatural like abilities.
Both have exceptional action sequences.

Though the story is totally differnt, the leads in both the series lead double lifes.
Nanban is slightly more hilarious.

Both have similar vibes, though the plot is slightly different.
Its about about school delinquents.
will be updated as this progresses.

Both the dramas are about falsely accused lead.
Much story Happens in prison.

Though the defendant is much much longer one and main plot is focused about the lead. And Joshu seven is slightly different as all the 7 prisoners back story is told.

Both are dealing with serial killers though I saw the devil has a revenge element in it.
Both has Cat and Mouse game between them.
(I saw the devil is much more gory and Insepctor Koo doesnt contain it)
(Inspector koo's serial kerial K kills the targets in such a way that it appears as an accident)

If you like "I saw the devil" try Inspector Koo, you might like it.

Both are dealing with serial killers though Signal has a Sci-Fic element in it.
Both have action, suspense, thriller elements.
If you like Signal, try Inspector Koo and there is good chance you would like it.

Both the movies have psycho killers, though cold fish's magnitude is much much larger.
Cold fish psycho killer is much more experienced and does targeted killing , though its slightly random in the Beautiful escape.
I would not dare to say beautiful escape will match CF, nevertheless it has similar dark plot and can be watched once.

Similarities:
A group of people trying to catch the culprits who generally escape from the police by using their connections or money.
Excellent Action sequences, suspense.
Both the leads acting is excellent.

Differences:
Taxi driver clients are based on someones revenge, its not the same in A as FL is trying to uncover a past incident.
In the A, they submit the culprits to law. A has slightly darker tone.

Highly recommed Avalanche if you like Taxi Driver.

WIll update , once the series is done.