Basil "Buzz" Nikvest operates as a lieutenant within Branch, a specialized covert unit of the AD Police tasked with investigating crimes involving advanced humanoid Boomers in futuristic Megatokyo. A widower since his wife's death at the hands of a rogue Boomer two years earlier, Buzz experienced a career-altering incident one year before the main events: while serving in the regular AD Police, he mistakenly identified a child as a Boomer and fatally shot them. This tragedy prompted his transfer to Branch and solidified his refusal to carry or use firearms, despite his recognized marksmanship.

Buzz authored the collegiate thesis "The Domino Effect Explosion system," analyzing urban crime patterns. This academic work later influenced Branch operations when antagonist Kenji Sorime applied its concepts to orchestrate the "Knights of a Round Table" attack.

Within Branch, Buzz maintains complex professional dynamics. His partner is Roy Kimball, a Boomer, creating initial friction due to Buzz's traumatic past; however, their working relationship evolves into mutual trust during investigations. Key colleagues include Reiko Michaelson, an agent who nurses unrequited romantic feelings for him, and Angel, a fellow operative with whom Buzz shared a prior romantic relationship. Chief Takahashi, Buzz's former college friend, leads the unit, though their relationship strains over time due to conflicting views on integrity and duty.

Across Branch's three interconnected cases spanning six years, Buzz demonstrates consistency in his core principles while adapting pragmatically. He upholds his no-firearms policy as a philosophical stance against violence towards humans and Boomers, preferring non-lethal deactivation of rogue androids where possible. This approach reflects his complex perspective on Boomers as more than mere machines, despite his personal losses. Nevertheless, during the climax of the final case, he abandons this policy in a decisive confrontation with the primary antagonist.

Buzz's demeanor remains predominantly stoic and duty-focused throughout this period. His character development manifests through his evolving partnership with Kimball and his handling of Michaelson's affections, rather than dramatic personality shifts. His professional commitment endures despite the traumatic events framing his backstory and the compromised ethics he encounters within the system.