The Host Turns Yandere (Quick Transmigration)

System Pipi was a conscientious little System in the Maintenance Department, devoted to finding a powerful Host to cling to. Then one day, in an apocalypse world, it spotted Qi Jiu: an IQ of 198, able to pass as either a female or male supporting character, and so awesome she even developed a drug to overcome the apocalypse virus. How cool was that? Looking at Qi Jiu, whom everyone adored, System Pipi made up its mind and bound itself to her. But things didn't turn out as it had imagined. Watching the powerful Host wave her hand and destroy yet another world, System Pipi trembled and hugged its chubby self, thinking its Host really ought to transfer to the Demolition Department. "H-Host, why did you destroy this world again?" Flames flickered across Qi Jiu's handsome face. She replied coolly, "Because I can't stand them." System Pipi could hardly believe that the Host who had saved the apocalypse was actually a world-destroying big shot. Then it found out that the drug used to eliminate the apocalypse virus could control people's minds... It had been so naive. Really. Qi Jiu had thought there was nothing worth staying for in this cold world. Then she saw a poor little thing who, though abandoned by the world just like her, still refused to give up hope. She watched with interest as he struggled through one world after another, gradually growing attached to him, until she finally made him the one and only object of her obsession... To Yan Fei, the figure who had single-handedly rescued him from despair was his only light. She would never know that if she had arrived a moment later, he would have become utterly unrecognizable... PS: It's probably the story of two yanderes saving each other. (The male and female leads are both yandere and don't share the usual moral standards.)