Nippon Noir: Detective Y's Rebellion

Both darker themed detective jdramas.
Male leads hold a secret while investigating.
Both have a supporting female character who takes an interest in male lead.

In both dramas, both main characters are unconventional/ controversial detectives who are involved in solving the deep secret within the police force. In both setting the organisations were involved in dark and unspeakable project that cost many lives and ending up affecting the lives of the main leads.

about human experimentation. also about the police and investigation. the human experiment gets discovered during an investigation. a lot of the characters die randomly and unexpectedly. a lot of twists and turns and the bad guy isn`t who you expect.