B: The Beginning unfolds on the islands of Cremona, where a vigilante known as Killer B is celebrated by some and hunted by others. Armed with a sharp blade and superhuman abilities, Koku takes justice into his own hands while a wave of crimes spreads across the archipelago, from stealthy executions of wrongdoers to sophisticated strikes on public figures. Unable to apprehend the renegade, the Royal Investigation Service (RIS) calls upon Keith Flick, a seasoned yet eccentric detective who was relegated to the Archives Department following a personal loss. As Keith studies the pattern behind the violence, it soon becomes clear that more than one person is responsible.
With the help of his impulsive sidekick Lily Hoshina, and with unexpected aid from the elusive Killer B himself, Keith begins to unravel plots involving secret organizations, domestic terrorism, and human experiments. The deeper he goes, the more the RIS appears involved in matters that extend beyond the scope of justice. Government corruption, along with the trustworthiness of close allies, is thrown into question as the hunt for a killer opens onto a wider conspiracy within Cremona.
