The Little Junior Sister Is so Gorgeous

Li Musheng is a homeless otaku. In order to raise money for his mother's surgery, he agreed to travel to the system to do a mission in the book "The Demon King of Destruction". The world was about to collapse because the heroine of the original book mutated and killed the male protagonist and beheaded the Heavenly Dao. The whole world is crumbling. His mission is to travel back to the time before the heroine was a monster and save everything.