Kuroino, also known as Blackie, manifests as a massive black tomcat with a distinct white crescent beneath his neck and a short tail culminating in a fluffy puff. His build evokes a bear's sturdy frame, complemented by narrow eyes featuring thin black slit pupils. In CGI portrayals, his whiskers shift from black to white.

He operates with stern independence, prioritizing his own rhythm over collaboration. Though his imposing demeanor unsettles many, he harbors deep loyalty and protectiveness, especially toward younger felines. His agility enables stealthy food theft from human dwellings—a habit from his past residence. He vigilantly marks and patrols his territory, defending it with fierce distrust toward humans.

Previously inhabiting an apartment complex, he routinely raided neighbors' units. One incursion into the Yamadas' home caused panic. Returning when only kitten Chi was present, he consumed her food despite her objections, groomed her fur, and departed.

With Chi, he forges a bond of unwavering mentorship, guiding her toward becoming a "real" cat through lessons on feline behavior and survival. He tolerates her exuberance, patiently walking her home and showing concern for her safety. During Season 2, he instructs Chi and fellow kitten Cocchi in pigeon-hunting after witnessing their failed attempts. He likewise endures playful kittens interrupting his naps.

His connection to Cocchi stems from mutual friendship through Chi. He respects Cocchi's diligence and intervenes to prevent him from fleeing during an escapade.

Across all official media—including the transition to the 2016 CGI series *Chi's Sweet Adventures*—Kuroino sustains a steady presence. While less frequent in *Chi's New Address*, his role intensifies in the newer series. His character evolution consistently emphasizes territorial guardianship and mentorship, retaining his core history and traits.