Rococo is a Fumoon, a new human race rapidly evolved on Bateito Island due to severe ecological devastation and nuclear pollution from atomic bomb testing.

She presents a small, fairy-like form with feminine eyelashes and tentacle-like appendages on her head. Entirely lacking a mouth, Rococo communicates solely through telepathy, embodying the Fumoon's insectoid-humanoid hybrid nature.

Her potent psychic abilities include telepathy for mental discourse and telekinesis for manipulating objects. These powers extend to controlling anti-gravity technology, enabling her to operate advanced Fumoon spacecraft known as "gondolas." Such capabilities are common Fumoon adaptations to their irradiated world.

During the Fumoon evacuation effort, Rococo assumes temporary command on Earth in leader Lady Mozu's absence. She oversees the critical collection of animal species for transport off-planet, a desperate mission against an approaching interstellar black gas cloud. This lethal cloud, born from a distant stellar explosion, threatens all Earth life with extinction.

Initially sharing her species' distrust of humans, whom she blames for environmental ruin, Rococo's perspective shifts dramatically after Kenichi saves her life during a Uran Union attack. In return, she defies other Fumoon to protect Kenichi, his sister Peach, and Detective Shunsaku Ban from execution, forging a bond of trust.

She later collaborates directly with Kenichi and human scientists to construct a planetary defense barrier against the gas cloud. When the electronic barrier proves insufficient, Rococo makes the ultimate sacrifice: merging her gondola's anti-gravity energy with the failing system. This act successfully deflects the lethal cloud, saving Earth's biosphere at the cost of her own life.