Rika learned robotics work from the fine people of Nakajima, and lived in Shrike for quite some time... Until a black-armored Maverick cut down all of her friends.
She swore revenge and joined the Maverick Hunters, working with them to eliminate -every- Maverick. However, after the Hunters were disbanded, she discovered that the Reploid who had murdered her friends was Seikou, who she had aided.
She tried to eliminate him, and in the process, met Vice. The two fell in love, and even weathered most of Jango's assaults together, but after Vice's death, Rika... snapped. She clad herself in Vice's armor and wandered the world, attempting to transform others into Vice along the way.
She joined the Militia in the hopes of getting her shot at Seikou, but was sidetracked along the way by meeting a rather insane Sniper Joe without an identity. Rebuilding him in Vice's image and giving him Vice's memory, she set off with him to defeat Seikou.
This also failed, and instead, Rika decided to settle down with Sniper Joe. However, visions she had awoke old fears enough to force her to flee from Wutai, as far as any one knows, she was never seen again.