Honkai: Simulation Across Myriad Worlds

How far can an ordinary person go if, with a System, they are cast into another world whose plot they already know? Qin Mo now had to find out for himself.

With the power of a simulator, he could play different roles in different worlds. He was a strategist, a calamity, a guardian, and a destroyer. Dreams, seals, death... As his footprints spread, his methods grew ever more varied. And on the battlefield reduced to ruins, he made himself the same promise for what might have been the umpteenth time: "The calamity of Honkai will come to an end, and humanity will seize a future that truly belongs to us."

(The Sin chapter wasn't written well. You can skip it and just read the two chapters at the end with the final results.) [Note: Not a mindless power fantasy, and not erotica.]