Gennai Hiraga is the Mobile Shinsengumi's resident inventor and scientist. He designs and constructs gadgets, weapons, and technological devices to aid the team against unlicensed monsters threatening Kyoto. His inventions frequently backfire spectacularly or prove hazardous, exemplified by a digging machine powered by unstable monster energy. Despite these frequent failures, some devices function as intended, showcasing his technical skill. He is also an acknowledged master chef with advanced culinary abilities.

Gennai operates with ruthless moral ambiguity, particularly during testing. He routinely forces the bakeneko Nekomaru to endure painful and distressing outcomes as an involuntary test subject for experimental devices. This treatment leads Nekomaru to declare Gennai more monstrous than the supernatural foes they fight. Gennai reacts menacingly to non-compliance; refusal to cooperate triggers a shift in his demeanor, marked by gleaming eyes and a deep, demonic rumble in his voice, revealing a capacity for intimidation. His visual design bears a noted resemblance to Dr. Tofu from Rumiko Takahashi's *Ranma ½*.

No concrete details exist regarding Gennai's origins, family background, or personal history. His character does not undergo significant development or reveal additional backstory across episodes or media. His role remains consistently focused on providing technological support—however erratic—through inventions, while his interactions emphasize his willingness to exploit others for experimentation and his threatening reactions to defiance.