Kirara Bernstein stands as the tallest senior member of the GJ Club at 180 cm. She possesses distinctive blonde hair styled into cat-ear shapes and blue eyes. Originally from Canada, her move to Japan caused a separation from her younger sister, Geraldine Bernstein, who later joined her. Kirara's Japanese language skills remain primitive due to her Canadian upbringing, contrasting her fluent English.

Her personality blends cat-like behaviors with a friendly disposition, extending a particular affinity to cats themselves, whom she can communicate with. Kirara exhibits enthusiasm for physical activities and sports, leveraging her exceptional strength—including a grip power exceeding 100 kilograms—and the ability to perform demanding physical tasks, positioning her as the club's enforcer for labor-intensive activities.

A defining obsession with meat drives her; she constantly eats it and fiercely protects it from others. Kyōya Shinomiya is the sole exception, with Kirara willingly sharing meat with him, indicating a unique bond. Her interactions frequently involve terse, fragmented phrases like "Meat?!", "Is this Meat?", or "Wanna eat?!".

Kirara harbors a significant fear of spiders stemming from a childhood venomous spider bite. She also displays low alcohol tolerance, becoming intoxicated after consuming liquor chocolates. Other weaknesses include sensitivity to being smelled and a dislike for vegetables.

Within the club, she shares her closest bond with Kyōya, extending beyond meat-sharing to actions like kissing other girls when intoxicated. Her familial bond with Geraldine is noted for mutual strength and affection, despite the initial strain of their separation. Kirara engages in typical club activities, such as tree-climbing, where her "cat" attributes excel. Her background, traits, and relationships remain consistent across media portrayals, including spin-offs like GJ-bu Chūtō-bu.