Mitzi Mouse was the younger sister of Atomic Mouse. She had a great childhood but always resented her overprotective brother. After finishing college, she met Mighty Mouse, the man of her dreams. They were married, and Atomic Mouse became great friends with his new brother-in-law. That was until she was mutated by Oil Can Harry, a crazy cat. Atomic Mouse blamed Mighty Mouse and the two fought. Mitzi sacrificed herself to save Mighty Mouse and Atomic Mouse and to defeat Oil Can Harry.