Not long after Ougai Mori takes the reins of the Port Mafia, his right-hand man, Osamu Dazai, has a nasty run-in with a gravity manipulator named Chuuya Nakahara, leader of the Sheep gang. However, with ominous rumors about Mori's deceased predecessor as well as the mysterious being called Arahabaki spreading throughout Yokohama, the duo must put aside their differences and get to the bottom of things. Before they achieved infamy as the fearsome pair Twin Dark, Dazai and Chuuya were just boys. Was their first encounter a harbinger of hope or an ill omen of things to come...?