The Genius Assassin Who Takes It All

Waking up as the main villain of his own novel was not part of the original plan. Now a lowly level 10 assassin, Ganghu Shin must use all of his prior knowledge as the author to navigate the fantasy world he created himself, and somehow alter the ending in order to return to the real world. Can he change the outcome and defeat the "real" villain to prevent his own demise and save this world from impending doom?