You must export the video as a series of stills (File > Export > Movie, then select setting, and change the file type to Targa or Filmstrip).

You will then need to apply rotoscoping to mask out the area you don't want. Do this by drawing around the anime character with your selection tool in a image editor such as Paint Shop, inverting the selection, then filling the rest of the canvas as black.

You can either save the selection as an alpha channel, or apply an alpha filter in Premiere once you've imported the images back to Premiere.

you can import a sequence of numbered stills back into premiere as video.