Kuro (クロちゃん Kuro-chan)- The main character who was kidnapped by Dr. Go and turned into a cyborg cat, along with various features and weapons. He has a horrible temper, and gets angry and out of control easily, but he is noble and good-hearted. He uses a gatling gun as a signature weapon.
Kuro was voiced by Chika Sakamoto.
Grandparents - The elderly couple who treat Kuro as a companion. They are not immune to trouble, never learn much, and are in need of Kuro's rescue frequently. However, they have no idea that Kuro is now a cyborg, though he intends to keep this secret.
Dr. (Mantaro) Go (剛くん Gō-kun) - The main antagonist and a major antihero, an eccentric inventor who wishes world domination by creating cyborg cats as weapons of mass destruction. His plan completely backfired when Kuro was created with a full will of his own. He later stops from his plans in world domination and decides to live in a more peaceful way of living with Mi and later Kotaro. He maintains a friendly rivalry with Kuro.
Dr. Go is portrayed by Tōru Furusawa.
Mi (ミーくん Mī-kun) - A cyborg cat created by Dr. Go to exterminate Kuro. He appears as a frequent "goon" of his but is in fact kind-hearted and noble. At a later part of the story where Go accepts defeat and turns down on his conquest to world domination, he is now often seen helping him and in times helping Kuro too. They are seen training together which often leads to them fighting for real which is to be stopped by Nana. Opposite to Kuro, Mi prefers a sword as his standard weapon. He can add himself to any weapon and additional items to them.
Mi was portrayed by Chiharu Tezuka.
Matatabi (マタタビ Matatabi) - An antihero, a regular cat who wears a red tattered "cloak" and has an eyepatch over his right eye, indicating injury. He was a childhood friend of Kuro, but he declared himself his enemy after assuming the cause of his problems was him. His main weapon is a wooden boomerang which he can use to hit targets at great distances. Whenever he is not fighting, he is seen hanging around on top of houses. He is skilled in craftsmanship and an experienced carpenter.
Matatabi is portrayed by Makiko Ohmoto.
Kotaro (コタロー Kotarō) - A boy genius dressed in a cat suit who helps Go and M out by assisting in their inventions or building his own. He has an obsession over Kuro, and tries to prove to be as powerful as him. This idea of his was the result of being an outcast. He is experienced in technology, with an IQ of 200.
Kotaro is portrayed by Rika Komatsu.
Nana (ナナちゃん Nana-chan) - A female robot with a cat-like appearance that was created by Kotaro from a table lamp. She develops a love interest in Kuro, who denies her; she accepts his rejection after numerous attempts to win his heart, though it is shown that he does care for her.
Nana is portrayed by Hiromi Tsunakake.
Ichiro Suzuki (鈴木 一郎 Suzuki Ichirō) - A schoolteacher who also admires Kuro. He is an avid otaku, and often gets himself involved into Kuro's shenanigans.
Suzuki is portrayed by Toshiyuki Morikawa.
Megumi (めぐみ Megumi) - A female firefighter who is Suzuki's secret crush. She is a quick thinker in most situations, such as putting out even the least dangerous of fires in her debut appearance in the anime.
Megumi is portrayed by Sayuri Yoshida.
Romeo is voiced by Kosuke Okano, while Juliet is voiced by Sayuri Yoshida.
Chieko Okada (岡田チエコ Okada Chieko) - A girl with a deep hatred for Kuro and very powerful supernatural abilities, including ESP and telekinesis. Another notable feature of hers is her voluminous hair.
Dunk (ダンク Danku) - Kotaro's robot friend. He was an ordinary lion, but he was involved in a near-death experience. Dr. Go successfully revived him in his current cyborg form. Dunk is quite timid, gentle, and pure.
He is voiced by Isshin Chiba.
YaYaYa Aliens (ヤーヤーヤー星人 Yāyāyā boshijin) - A trio of friendly aliens that boast incredibly dangerous weapons. They are often also seen wearing special bracelets that can enlarge or shrink their targets.
Goro Nagase (長瀬 五郎 Nagase Gōrō) - A boy Chieko met once. Goro came from an abusive household. He is a big dreamer, but he is a loser. He boasts a large scar from his abuse.
Prince Malo (マロ王子 Maro-ōji) - A prince of the YaYaYa group. He bears a striking resemblance to Kuro. Malo is supposed to be courteous and he has the opposite personality from Kuro, but he eats like a vampire, and he also boasts offensive British gas.
He is voiced by Chika Sakamoto.
Princess Mimi (ミミ姫 Mimi-hime) - A princess who looks exactly like Nana. Malo was supposed to marry her, but he refused. Despite her ladylike looks, she is actually quite selfish.
She is voiced by Hiromi Tsunakake.
Nyan-Nyan Army (ニャンニャンアーミー Nyannyanāmī) - A squadron of cyborg cats created by Dr. Go. Mi is the first in the line, created by Go from the remains of his pet kitten.
There are four other members:
- #2 (Nicknamed Spyder), who can expand his arms, legs, and neck. He is voiced by Yuko Sasamoto.
- #3, who also fights with his own sword and boasts a panda disguise. He is voiced by Rika Komatsu.
- #4, who also has a bad temper and is the most frequently encountered. He is voiced by Sayuri Yoshida.
- #5, who is seen with a robot companion, Lassie, and also uses a gatling gun. He is voiced by Mami Nakajima.
Tendou (天道 tendo) - The main enemy and rival of Doctor Go, and the guy responsible for the demise of Mi's mother. Unlike Go who's allies are cats, Tendou prefers to use dogs.
He is voiced by Naoki Tatsuta.