Tensei Shitara Slime Datta Ken, known in English as That Time I Got Reincarnated as a Slime, is an isekai light novel and anime about a man who dies and is reborn in a fantasy world as a slime, using his new powers to build a nation of monsters and diplomatic alliances. Its worldbuilding-heavy take on isekai made it one of the genre's biggest hits. Slime hentai doujinshi are a popular fixture of that fandom.