Miyuki Koizumi works as the school clinic nurse alongside Dr. Haruka Nishikikōji. The two share a deep friendship dating back to their childhood. Her duties involve assisting in the clinic and frequently stepping in to resolve chaotic complications caused by Dr. Haruka's malfunctioning, unconventional inventions; she demonstrates significant competence in mitigating these incidents.

Miyuki is a proficient martial artist with competition victories to her name. Her younger sister, Mayumi Koizumi, attends the same school where Miyuki is employed. While maintaining a professional working relationship with Dr. Haruka, their history includes his repeated, unsuccessful attempts to express romantic interest in her, typically through inventions that fail due to technical issues or unintended consequences. Miyuki remains supportive despite these recurring events.