Coco is a teenage girl that died in a gruesome car accident. Without the knowledge or consent of her parents, her brain was extracted from her body by a secret government agency and planted into a giant robot body. Naturally, Coco had some reservations about this upon waking up, which were promptly ignored.

Coco was presented to Hillary Boson (you all remember her, right? Go look her up if you don't) as a sparing partner and friend. In reality, Coco was designed to keep an eye on Hillary and, if needed, take her out.

Hillary gets along with her fine, but it's apparent that Hillary can handily kick Coco's ass. Hillary doesn't seem to have any idea about Coco's real purpose, though.

Coco was made about 10-20 feet taller than Hillary so she could "grow into her", so to speak. Also because giant robots are kind of expensive to build, and they can't make her that much bigger on their current budget.