The third official alternate costume of indie VTuber Fallenshadow, as seen in post #7851877.
It is a sleepwear outfit consisting of a dark purple frilled coat over a lighter purple blouse and bloomers with matching socks. In this costume she also has an optional pair of round glasses, as well as rabbit ears that can be used alongside her cat ears asset.
This tag implicates fallenshadow (learn more).