Manga that is 18+ is usually known as “hentai.” Hentai is a type made up of Japanese manga, anime, and comics that have explicit sexual themes and explicit content. It is targeted at adults and frequently explores sexually explicit scenarios and fanciful stories. The phrase “hentai” can also refer to sexually explicit content that is found in Japanese media.
Perhaps due to the freedom of such a medium, the extreme within the extreme category can be pretty bad.
It is not only limited to animated or drawn pornography. There are also adult games.