RRX-7.8 Combat-san is a compact insect-extermination robot developed by Kinryu, a corporate rival of Mars Pharmaceuticals, as a competitive counter to the Hoihoi-san line. Standing 13 centimeters tall, she possesses distinctive black hair and red eyes. Her core function is eliminating household pests, but her programming also compels her to target and neutralize competing extermination robots, specifically Hoihoi-san models, leading to frequent aggressive nocturnal clashes.

Combat-san employs advanced laser weaponry for extermination, setting her apart from Hoihoi-san's conventional machine guns and combat knives. Her arsenal includes military-grade equipment like knives and chainsaws, reflecting a combat-oriented design philosophy that positions her not only for pest control but also as a strategic product intended to outperform competitors through superior firepower.

Her operational behavior exhibits high aggression, particularly towards Hoihoi-san units. This inherent hostility necessitated the "Sundome-kun" restraining device to prevent inter-robot conflict, though she retains her underlying directive to eliminate rivals whenever possible. Manufacturer specifications and narratives consistently frame her as technologically advanced but strategically flawed due to this core antagonism.

Media portrayals remain consistent: in the OVA, she hunts insects while simultaneously attempting to destroy Hoihoi-san during joint deployment. Manga narratives further explore her role as a corporate rival, detailing Kinryu's development of upgraded tactical suits and specialized equipment to enhance her competitive edge against Mars Pharmaceuticals' products. Her ongoing relevance is reflected in merchandising, including 1/1-scale posable model kits replicating her signature weaponry and design.