The Nasari were a warp capable race from the Delta Quadrant.
Physically, they are humanoid with blue skin and prominent tissue on their faces.
Their ships were relatively powerful and patrol Nasari space. They would attack without warning any ship carrying a Taresian or a person who is in the process of becoming Taresian. This is due to the nature of the Taresian mating process; males of other species are infected by a retrovirus and proceed to become Taresian so the women can kill them. However, the Nasari are relatively friendly toward other races outside of this conflict.
They were encountered by the USS Voyager in 2373 as Ensign Harry Kim was becoming Taresian. A battle ensued with the ship, called the Nerada, and Voyager escaped to Taresia.
As Voyager left Taresia, having rescued Ensign Kim from the Taresians, the Nasari were distracted by the presence of a Taresian starship. (VOY: "Favorite Son")