[Shiromitsu Daiya] Dokidoki Costume Play (Koushoku Shounen Vol. 10)

A pair of crossdressing brothers debut their matching catboy cosplay at a convention—twintails, rubber gloves and all—then head home to put those costumes to filthier use, with teasing nipple play and a tail plug giving way to filmed anal sex. The younger brother can't resist directing his slippery Nii-chan in front of the camera, urging him to show off exactly where they connect while insisting the stream is already off. The punchline lands when they realize the broadcast never stopped, and the two spend the walk to school the next day praying nobody stayed until the end.