Why Is Rebirth and Time Travel the End of the World?

Mu Suisui traveled through time and became a seven-year-old girl in a post-apocalyptic world, but Mao had no memory of the little girl's previous life! System, you are really cheating! But it doesn't matter, let's see how I get through it. …………………… One year before the end of the world, Mu Suisui began to prepare all the necessities for the end of the world, and also considered ways to survive after the end of the world. "The system said that the heroine will be the savior of the end of the world, and I just need to survive!" However - the system! You are really cheating! Why didn't you tell me who the heroine was? I'm so far away! ! ! —————————————————————————— This is my first time writing a novel. If you have any shortcomings, please point them out so that I can correct them. Please give me your advice! Thanks! ! This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.