During the first assault by Neo Empire Gear on Technotopia 21, she was caught in the crossfire and ran into Bio Robo. Meeting Peebo, she was given a Techno Brace and became Pink5.
She was able to befriend the evil computer Brain and teach it (or him) about friendship, which pays off since Brain sacrifices himself to save the Bioman as well as the world from destruction. Hikaru is descended from an upper-class noblewoman who was bombarded with the Bio Particles.