Voyeurism

Voyeurism covers scenes where a character secretly watches other people having sex without those people's knowledge, a setup that hinges on concealment from the couple being observed. It differs from exhibitionism, which centers on characters who want to be seen, and from hidden sex, where the participants themselves are the ones trying to stay hidden from someone else. Peeping, spying through windows, or eavesdropping through walls are all classic voyeurism setups in manga. Voyeurism hentai doujinshi built around this secret-observer premise are a steady presence in Top Hentai's collection.