The Great God Pan
The Great God Pan is a horror and fantasy novella by Welsh writer Arthur Machen. Machen was inspired to write "The Great God Pan" by his experiences at the ruins of a pagan temple in Wales. What would become the first chapter of the novella was published in the magazine "The Whirlwind" in 1890. Machen later extended "The Great God Pan" and it was published as a book alongside another story, "The Inmost Light", in 1894. The novella begins with an experiment to allow a woman named Mary to see the supernatural world. This is followed by an account of a series of mysterious happenings and deaths over many years surrounding a woman named Helen Vaughan. At the end, the heroes confront Helen and force her to kill herself. She undergoes a series of supernatural transformations before dying and she is revealed to be the child of Mary and the god Pan.
God Mazinger
The manga, although it shares some similarities and the same premise, differs from the anime with a more mature tone and also has a different conclusion. It was originally published in tankōbon format by Shogakukan in 1984. It was later re-printed in 1986 by Kadokawa Shoten under the title of "Majin Densetsu" and also under the original title by Chuokoron-sha in 1995 and Daitosha in 1998.