About the Fact That I Want to Eliminate Gherroth

[Cthulhu][No system][Single female protagonist] Jiang Fan, who was terminally ill and on the verge of death, was dragged into a different world on his eighteenth birthday. The visitor told him that he was the chosen one who was prophesied to kill "Gheroth". However, because of his own weakness, he could only be exiled to a place of comfort - the Nineteen Pools of the Abyss. How can he, abandoned by the world again, go from the bottom of the abyss to the destined throne?