Geraldine Bernstein, nicknamed Jill, is Kirara Bernstein's younger sister. After Kirara moved to Japan, Geraldine lived alone in Canada before relocating to join her. She possesses bright blonde hair and blue eyes with yellow linings, typically wearing a school uniform with a cream-colored cardigan and blue ribbon—though the anime adaptation replaces ribbons with pins and alters the uniform ribbon to yellow. Her side-bangs feature three ribbons (pins in anime), and she often pairs the uniform with knee-high socks. Geraldine communicates exclusively through a small whiteboard and marker, understanding and writing Japanese but unable to speak.

She reveres Kyōya Shinomiya as her "Samurai Master," a title originating from his aid during their first encounter, and consistently addresses him as such. Her physical strength mirrors Kirara's, demonstrated when she effortlessly lifts her sister.

Geraldine is a main character in the GJ Club Junior High School Division (Chūtō-bu) spin-off GJ-bu Chūtō-bu. She shares a classroom and close friendships with Kasumi Shinomiya (Kyōya's sister) and Seira Amatsuka, frequently appearing alongside them. Through Kirara, she connects to the original GJ-bu club, appearing secondarily in light novel and anime adaptations.