Kuroino, also known as Blackie, is a large, black male cat with a distinctive white crescent-shaped marking beneath his neck and a short tail ending in a fluffy tuft. His build is often described as bearlike. He possesses narrow eyes with thin black slit pupils. In CGI adaptations, his whiskers appear white instead of their original black.

Independent and preferring his own pace, Kuroino maintains a stern, serious demeanor. He is not easily intimidated, traits others initially find frightening. Beneath this exterior, he shows compassion, loyalty, and a protective instinct toward those he cares for. Highly agile, he is skilled at stealthily entering human dwellings to steal food, a behavior established before his relocation. Territorial by nature, he diligently marks and patrols his domain and harbors a general distrust of humans.

He previously inhabited an apartment complex, frequently raiding neighboring residences. During this time, he intruded into the Yamada family’s apartment, causing alarm. On a subsequent visit, he ignored Chi’s objections to eat from her food bowl and stayed briefly to groom her before leaving.

Kuroino acts as a mentor and guardian to Chi, consistently guiding her toward understanding feline behaviors to transform her from a "silly kitten" into a "real" cat. Despite her energetic nature, he remains patient, offering advice about the cat world and ensuring her safety, including escorting her home. His bond with Cocchi stems from their mutual connection to Chi; Kuroino respects Cocchi’s diligence and has intervened to prevent him from running away.

He appears across the series, featuring in most of the first season, select episodes of *Chi’s New Address*, and the majority of the 2016 CGI installment *Chi’s Sweet Adventures*. He habitually says "later" when departing. His Japanese name, Kuroino, translates to "the black one."