"The Saga of Tanya the Evil" is a Japanese light novel series written by Carlo Zen. It follows the story of a salaryman who is reincarnated as Tanya Degurechaff, a young girl in an alternate world resembling early 20th-century Europe. Tanya is a powerful mage and serves in the military, where she seeks to climb the ranks while battling against various nations and magical threats. The series explores themes of war, ambition, and the consequences of one's actions. Tanya's ruthless and pragmatic approach to life often leads her to confront the Being X, a mysterious entity that challenges her beliefs and existence. The story has been adapted into manga and anime formats, gaining popularity among fans.