I'm Just a Hereditary Prison Guard, and You Want Me to Revive Humanity?

[Genius power progression + slow-paced + invincible among peers + decisive and ruthless + cunning + playful banter + lighthearted daily life] In the boundless wilderness, countless races stand side by side. Lu Qingyun accidentally transmigrates to the Yuhua Divine Dynasty and becomes a hereditary prison guard. He slays a demonic beast from the start and obtains the Lifespan-For-Slaying-Monsters System. [Slay a Colorful Dawn Chicken, gain 40 years of lifespan] [Slay a Long-Eared Spirit Rabbit, gain 100 years of lifespan] [Slay…] He can also spend his lifespan to evolve things without limit. His natural talent keeps evolving… From ordinary to divine! His skills keep evolving… … “I can tell you have excellent spiritual roots and a unique constitution. You’re a once-in-a-thousand-years genius. The task of revitalizing the human race will have to fall to you…” By “coincidence,” the princess of the Divine Dynasty sends him an unparalleled cultivation technique. Before Lu Qingyun even gets the chance to experience its evolution, he has already mastered a peerless art! But he can’t help asking: “I’m just a prison guard. You want me to revitalize the human race?” … Until the day the myriad races invade! The Divine Emperor is missing, and the Yuhua Divine Dynasty teeters on the brink of collapse! Seeing the human people’s suffering, Lu Qingyun resolutely steps forward, fearing neither danger nor death! He turns the tide when all seems lost and saves a collapsing empire! He’s cautious, but he isn’t afraid to die! As the saying goes: “Slay a million troops of the demon race, and I’ll gladly save the human race from ruin!” (The synopsis doesn’t do it justice, so please read the story itself. I hope the great readers will add it to their bookshelves and try a few chapters. I’m begging you! Please be gentle…)