In a world where Earth has entered a supernatural era, all things evolve, and monsters run rampant, humans awaken their star souls during evolution to fight against the rampant monsters. Zhou Xuan, a handyman at the Demon Suppression Tower, unexpectedly awakens an unscientific check-in system. He checks in on ancient ferocious beasts and obtains primordial power; he checks in on weed spirits and his star soul evolves into a Nine-Leaf Sword Grass. Millennium Xuanwu, ten-thousand-year Sea King, immortal Vermillion Bird, and Heaven-Devouring Dragon all become his check-in targets. "Ding, target detected—Heaven, do you want to check in?" "Ding, you successfully checked in on Heaven and obtained the laws of Heaven." Heaven: Huh?? Then I'll be going??? On that day, the demon god awakened, and Zhou Xuan, using grass as a sword, struck down the demon god's soul with one strike. This book is also known as "I Learned to Slay Gods Inside the Demon Suppression Tower."