Known as "Black Bear Cat," Blackie (or Kuroino, meaning "the black one" in Japanese) is a large, black male cat bearing a distinctive crescent-shaped white marking beneath his neck and a short tail tipped with fluff. His bearlike physique features narrow eyes with thin black slit pupils. Earlier portrayals depicted him with black whiskers, while later CGI iterations show them white.

Blackie maintains a stern, serious, and independent demeanor, moving at his own pace and resisting delays. Many initially find him intimidating, yet beneath this exterior lies a fiercely loyal, compassionate, and protective nature. Highly agile, he once specialized in silently infiltrating homes to steal food—a regular habit before relocating. He vigilantly marks and patrols his territory, defending it with intensity, and typically distrusts humans.

Originally residing in an apartment complex, he frequently raided neighboring units for sustenance. During this period, he invaded the Yamada apartment, alarming its residents. On a later visit when Chi was alone, he consumed her food despite her objections, then briefly groomed her fur before leaving.

His bond with Chi Yamada defines his core role. He consistently mentors her, guiding her toward becoming a "real" cat rather than a naive kitten. Patient despite her energetic and troublesome tendencies, he shares feline wisdom, prioritizes her safety by escorting her home, and imparts crucial lessons.

Through Chi, Blackie connects with another cat, Cocchi. He respects Cocchi's work ethic, watches over him, and notably intervened to prevent Cocchi's attempted escape during series events.

Across installments, Blackie appears extensively in the first season, sporadically in "New Address," and returns as a regular in the 2016 CGI revival. He habitually exits scenes with the word "later."