Kuroneko is, as her name suggests, a black cat. Yasuhiro Nightow has said that the cat is female. Kuroneko-sama is a small black cat with big green eyes, and not much is known about Kuroneko-sama's personality, but she acts like a normal cat.

She appears in every episode of the first anime and randomly in the manga, usually as a running gag, popping on screen at some opportune moment and uttering a simple "nyaa." Despite her level of recurrence, Kuroneko-sama has had few instances of plot significance. She stopped Wolfwood from cheating in a game of chess during the episode "Escape from Pain" (and also when Vash is replaced by her in "Hang Fire"). Nightow has stated that she is just something easy and calming to draw in between action scenes. His most common response to queries as to her nature or significance at anime convention panels is "Kuroneko-sama is a small black cat."

In Trigun Maximum, Kuroneko only appears in Nightow's commentary at the end of each issue, often criticizing the author's lazy and silly nature.

In Trigun Badlands Rumble, Kuroneko can be first seen napping at the newsstand where Vash finds out he is blamed for Gasback's bank heist. The cat can be seen again, watching Meryl and Milly as they discuss their situation with Cain's statue. Also, during the bar fight later in the film, Kuroneko flies through the air along with many other items, seemingly thrown by someone as a projectile.

Kuroneko-sama also makes a small cameo appearance in some Kekkai Sensen and Kekkai Sensen & Beyond episodes.