Set in the floating archipelago nation of Cremona, the gripping adult anime series *B: The Beginning* centers on a cryptic string of murders committed by the elusive serial killer known only as "B." The Royal Investigation Service (RIS), a specialized police force, is tasked with stopping him. RIS brings back legendary, eccentric investigator Keith Flick, whose brilliant deductive mind immediately sets him apart from his peers. Meanwhile, a mysterious young man named Koku works quietly in a violin workshop, harboring a secret identity and a desperate personal mission: to rescue his childhood friend, Erika, who was abducted years ago by a shadowy, cult-like organization.As Keith delves deeper into the "Killer B" cases, he uncovers a massive conspiracy involving the royal government, a shadowy cabal known as the Market Maker, and supernatural beings called Reggies—humanoid creatures genetically engineered to possess immense, monstrous strength. It is soon revealed that Koku is actually "Black," the prototype Reggie created to lead their kind, and his rampage is driven by a quest for vengeance against
the organization that stole his peaceful life.Parallel to the
police investigation, a dangerous domestic terrorist cell named the RIS Executioners plots to destabilize Cremona, forcing Keith and Koku’s paths to violently and fatefully intersect. Koku possesses the unique ability to transform into a horned, demonic entity, making him both a prime target for the Market Maker and a terrifying threat to the city. Despite initial hostility, Keith and Koku form an uneasy alliance. Keith recognizes that the royal family's corrupt prime minister is using the Market Maker's experiments to create an invincible army, while Koku simply wants to reclaim his humanity and save Lily Hoshina, a kind-hearted RIS rookie who bears a striking resemblance to Erika.The narrative escalates into a brutal, high-stakes war within the underground lab facilities of Cremona. Betrayals are uncovered within the RIS ranks, and Keith confronts his own tragic past regarding the murder of his younger sister, Erica, which shares eerie parallels with the current conspiracy. In the explosive climax, Koku unleashes his full, devastating power against the ultimate Reggie creation, yellow-eyed antagonist Gilbert. Through cunning intellect and emotional sacrifice, Keith dismantles the corrupt political infrastructure, while Koku finally finds closure. Ultimately, the series concludes with the corrupt powers neutralized, leaving Keith to return to his solitary life of contemplation, and Koku walking away to seek a quiet future alongside Lily, finally free of the curse of his monstrous origins.