Joker Yurusarezaru Sousakan (2010)

Both feature Sakai Masato as a main character who seeks justice by exposing crimes.

Both have antihero, police officer male leads who punish criminals who escape the law. They deal with themes such as morality, justice, and the fallible legal system. Also similar to the 2023 Korean drama Vigilante.

- Main character/s aren't good but they aren't evil either - Injustice - Main character/s have a dark hidden past that's connected to the plot

Both of them has a dark side of police force. Each episode add clues for main plot.

While the two series weren't quite similar aside from the common crime/investigation genre, there was at least one common trait. As in, the fact that both dramas featured Nishikido Ryo as an eccentric forensic officer/expert. And for people who're a fan of the actor, it'll be interesting to see how Ryo's character differed in Joker as compared to Trace.

both deal with questionable police practices, also in both the main leads have some sort of dark secret.

The leading character in both dramas are very similar. Both characters sometimes use unlawful means to punish the guilty.