Prostate massage is an act tag describing internal stimulation of the male prostate gland, typically performed by a partner as a specific sex act distinct from general anal content. It's tagged separately because the prostate-focused stimulation itself, rather than penetration in general, is the point of the scene, and it often appears in femdom or medical-play-adjacent stories. The tag applies to a well-defined, real anatomical act rather than a fantastical trope. Prostate massage hentai doujinshi covering this act are searchable within Top Hentai's manga library.