'S' only applies to English.
Them Nips have a habit of romanizing names base on the source language, and in this case Cybele is indeed pronounced with a 'K' - Kybele, in Greek. That being said, this doesn't excuse Nips' bizarre habit of romanizing many things with '-y-' using 'yu'... resulting in Kyu~bere (QB), Pyu~ton (Python), Tyu~pon (Typhon) and the likes