In Cremona's islands, a vigilante known as "Killer B" is wreaking havoc. While some hail the sharp-bladed, superhuman avenger as a hero, others are after him. Despite their efforts, law enforcement – represented by the Royal Investigation Service (RIS) – have failed to capture the elusive Killer B. To help them, the RIS brings in an unorthodox detective named Keith Flick. Though his peculiarities got him transferred to the Archives Department after a personal tragedy, Keith's unmatched skills make him the perfect match for the case. As the situation in Cremona becomes more dire than ever – with the vigilante's stealthy assassinations and targeted attacks on public figures – Keith and his impulsive assistant Lily Hoshina realize that Killer B might not be the only perpetrator. Together, they uncover a complex web woven by secretive organizations, domestic terrorism, and sinister experiments on human subjects. However, as they dig deeper, the extent of the government's complicity in the crisis becomes clearer – and so do the risks of trusting even the closest of allies.