Hotaru is a descendant of the Fujibayashi clan, one of the three influential branches of the Iga ninja. Her father taught her how to transform, but both he and her mother died when she was six years old. She would have kept crying at their tombstone, but Momoji was ordered by their village elder to take care of her. He raised and trained her as his sole apprentice.

Though his training was strict, Hotaru enjoyed a happy childhood by his side. When she was twelve years old, Momoji mysteriously left the village on a mission without saying goodbye to her. His sudden departure was painful to her, yet it simultaneously encouraged her to continue her training with renewed interest. She felt she needed to honor his teachings in his absence. Out of the ninja in her village, she became the most proficient ninja with transformation spells. She arms herself with kunai when she wishes to defend herself.