Not much to say, honestly. Both are about violent cops: «Hana-Bi» is deeper whilst «Violent Cop» could be defined as a regular crime movie.
Hana-Bi (1997)
Related
Both films were directed by Takeshi Kitano; and he's also the ML in both of them. Both feature a burnt out ML who burnedened by his worries begin a downward spiral
The main character is a tragic and melancholic old man who has lost everything and whose only way of living is with violence.