文豪ストレイドッグス　太宰治と黒の時代 (light novel)

It's been roughly one year since Chuya Nakahara joined the Port Mafia, and he's got his sights set on an executive position. But as he makes plans to move up, a man by the name of Paul Verlaine--claiming to be his younger brother--appears and vows to assassinate everyone he cares about! Now, Chuya must team up with Adam, a European A.I. investigator, to stop this lunatic before the storm swallows Yokohama once again...