Romio is Ayeka's incarnation from Magical Project S and the true antagonist of the series.
Romio is the third candidate to be the queen of Juraihelm. After she loses, Romio disappears from the scene for a time, later appeared before Ramia to help her become queen after Pretty Sammy had restored the balance between Earth and Juraihelm, with Tsunami about to be crowned queen.
Much to Rumiya's protests, Ramia accepted Romio's offer and Romio kidnaps Eimi Date (Sasami's classmate) and turns her into her own magical girl, "Love-Me Eimy", for her plan to drain Juraihelm and earth of all magic. When that fails, Romio revealed her true self to Ramia and attempts to drain Juraihelm's magic with her NT System and use the stolen magic power to send the earth into the sun.
It turns out that Romio was once a magical girl but was unable to fix the balance between Earth and Juraihelm, and since then she has felt the Earth is evil and wants to destroy it. Romio's plan is stopped by the combined might of Pretty Sammy, Pixy Misa, Ryo-Ohki, and Rumiya with the assistance of Professor Washu, who develops her own NT System.
After her NT System is destroyed, Romio is carried off into the distance by an angry Ramia. At the end of the series, despite her defeat, Romio hasn't given up and is now leading the Martians against Earth, as Pretty Sammy and Pixy Misa move in to stop her.