Ouroboros: Keisatsu wo Sabaku wa Ware ni Ari

At first glance Ryuzaki Ikuo, a detective in the Shinjuku Police Department's 2nd detective unit, & Danno Tatsuya, a high ranking member of the Matsuo Yakuza clan have nothing in common. However they both are working themselves up the ladder in their respective careers for one reason which deals with a murder case that happened 15 years earlier of which both men were witnesses to.