Bungo Stray Dogs, Vol. 8 (light novel) - Storm Bringer

It's been roughly one year since Chuuya Nakahara joined the Port Mafia, and he's determined to become an executive before fellow mafioso Osamu Dazai. However, a man by the name of Paul Verlaine-the king of assassins who claims to be Chuuya's older brother-suddenly appears, vowing to murder everyone he cares about! Now Chuuya must team up with Adam, an AI investigator from Europe, to stop this madman before another storm engulfs Yokohama. Along the way, many truths will be revealed...including the answer to Chuuya's most pressing question: Is he himself even human?