Ouroboros: Keisatsu wo Sabaku wa Ware ni Ari

Ryuuzaki Ikuo and Tatsuya Danno once belonged to a happy family of orphans at the Mahoroba Orphanage. Their beloved teacher, Yuiko, cared for and nurtured them; to Ryuuzaki and Tatsuya, she meant the world to them. Thus, one late night, their whole world fell apart when they witnessed her tragic murder. Though the young pair testify that a man shot their teacher, the police force them to keep quiet. And so, they realize that this murder case contains a darker truth, one hidden by the authorities. With no one else to trust, Ryuzaki and Tatsuya decide to work within the shadows to catch the seemingly influential culprit. Even if they end up dirtying their hands, the only justice that matters to them is the truth behind Yuiko's death. Fifteen years later, Ryuzaki joins the Shinjuku Police force and becomes the second department's top investigator, while he secretly works with Tatsuya, who is now a high-ranking member of the yakuza. Fueled by vengeance and love for their teacher, the two friends join forces to find the culprit, vowing to exact revenge upon the evil who took their world away.