Xiaozhi's family was invaded by alien Zerg. The alien Zerg lurked on the earth and gradually devoured the relatives and friends around Xiaozhi's family, sparing none of them one by one.
Xiaozhi was not invaded by the Zerg. After her brother was invaded by the Zerg, he still retained a trace of himself and secretly protected Xiaozhi from being harmed by the Zerg.
Xiaozhi thought she was mentally ill because she could always see the existence of insects. Xiaozhi's family also tried to use mental illness as an excuse to explain why she could always see insects.
However, paper cannot contain the fire.