Mimika Washizaki is a classmate and close friend to Misha Takanashi. She has straight-cut bangs and naturally wavy hair, typically braided to manage the curls, along with round glasses and thick eyebrows. She prefers modest, simple clothing, sometimes featuring cat patterns. As she grows older, her hair lengthens, maintained in long braids with a front bob cut.

Gentle, quiet, and caring, Mimika acts as a dependable older sister to her two younger brothers, showing loyalty and responsibility. Despite her kindness, she displays occasional naivety, such as believing superstitions or unfounded rumors; she once drank iced coffee before a sports event hoping to fall ill, only to become fatigued. She excels academically but struggles in art and physical education.

Initially overlooked due to her plain appearance and reserved nature, Mimika began delivering school handouts to Misha's home during Misha's absence following her mother's death, forming the basis of their friendship. Their bond solidified when they served together as class animal keepers, particularly during an incident caring for newborn hamsters, leading Misha to trust her completely and affectionately nickname her "Washiwashi."

Mimika overcame personal insecurities about her glasses and bushy eyebrows. She gained confidence after Tsubame Kamoi complimented her appearance and encouraged her to wear a frilly dress, prompting Mimika to adopt glasses with decorative flower frames. Her resilience showed during a sleepover at Misha's home, where she revealed unexpected pillow-fighting skills honed with her brothers, declaring her prowess mid-fight.

Her interests center on cats, reflected in her collection of cat-themed bags and clothing. For her birthday, Misha considered a cat-themed gift but instead baked homemade cat-shaped cookies with her, valuing shared time. Tsubame also gifted her a frilly dress with cat ears and a tail.

Maintaining her academic diligence and friendships beyond elementary school, Mimika decided to become a preschool teacher by high school graduation. She enrolled in a national university in Tokyo to study education, continuing to live with her family. She occasionally expresses light envy toward peers living independently but remains closely connected to her childhood friends.