Uni the Black Cat

Uni is a formerly-stray black cat that is occasionally seen playing with Kyuu-chan. He is first seen in chapter 403, "Intrusion." Later, the Security Guard gives him the name Uni.

Appearance
Uni is a black cat with white paws and white around his mouth.

After being adopted by the Security Guard, he wears a pink collar with a bow.

Personality
Uni has a rather prickly personality, hissing at people and avoiding others. He does however, warm up to people eventually, such as with Kyuu-chan and the Security Guard.

Story
Uni first appears when he hisses at Hinata and Kyuu chan while they're at the park. Kyuu-chan realizes he is hurt, and uses one of his socks to bandage his paw. Uni immediately runs away, then comes back another day to give Kyuu-chan a flower in thanks before running away again (Chapter 405, "Thank You").

Later, Uni meets the Security Guard and apparently ends up being adopted by him (Chapter 516, "A Place to Call Home").

Kyuu-chan
Kyuu-chan first helps Uni when he injuries his paw, bandaging it with his sock (Chapter 404, "Mr. Black Cat"). Afterwards, Uni begins to hang around Kyuu-chan and the two become friends. Kyuu-chan often appears to help Uni when he's in trouble, such as slipping off a wall, or slipping on the ice.

The two later play in the snow together (Chapter 535, "Snowman Builders").

Security Guard
The two first meet when both of them hide to avoid socializing with others. Uni, recognizing the Security Guard's behavior, sees him as a kindred spirit and nuzzles up to him (Chapter 513, "In the Shadows"). He starts to hang around the Security Guard's work after that, and the Security Guard soon adopts him and gives him the name, Uni.

The two of them have similar personalities, both appearing hostile and intimidating, while actually being very softhearted inside.

Trivia
"Uni" means "Sea Urchin" in Japanese, potentially referencing his hostile exterior.