The end of the "cat gap" on Terra is probably explained by the introduction of Pseudaelurus from the Zhdez homeworld, where cats appear continuously in the fossil record. If the Precursors did the same on the Inukari homeworld, they failed to establish. Instead, mustelids occupy most of the niches that felines do on the other two human homeworlds. Thus, the early Inukari chose a mustelid to domesticate for pest control: the kuga.

The baseline kuga is similar to, though larger than, a Terran domestic ferret, but comes in a far wider range of sizes and fur types. Long-haired kugai can look almost skunk-like, though domestication resulted in selecting for musk strength closer to a Terran tomcat's so the similarity is limited. Juvenilization has resulted in larger eyes and ears, and blunter muzzles.

As with other pet species, kugai have been bred for a variety of sizes, and cross-bred with related wild species. A "teacup" kuga is closer to the size of a domestic rat, though its lifespan is about half that of the larger kugai. Kugai descended from livestock-protection breeds are larger than the usual, still rarely more than twenty pounds, and tend to be poorer housepets.

Aboard starships, they are kept for companionship but also for hunting the inevitable rodents that find their way aboard from dockside. These tend to be the smaller types, well able to follow anywhere a rodent can go.