What exactly is Chūya Nakahara—? The story of Twin Dark's "Sixteen" shall now unfold. It has been a year since Chūya joined the Port Mafia after ending the "Arahabaki Incident" with Osamu Dazai. As he aims for the executive position, a man named Paul Verlaine appears before Chūya, calling him his younger brother! "I will kill anyone who intervenes with your heart," he announces. To thwart his plans, Chūya teams up with European artificial intelligence investigator, Adam. The sign of a storm waiting to swallow Yokohama brews once again. What exactly is Chūya Nakahara: the truth of the past shrouded in darkness shall now be revealed—!