Stardust's owner adopted a retired Medical Grade Helper. Medical Grade HelperBots (MGs) are as the name suggests, made for people who need assistance with their medical conditions. Medical Grades come only in standard Sun and Moon models, and they're bigger and stronger than regular HelperBots with more memory space for the needed knowledge. You can only get a working MG if you have a good insurance for your medical condition. Or by adopting a retired one, like Stardust's owner did.