Mecha Shenyi

This is a human civilization rebuilt from the ruins of nuclear war. There is no country, no race, no capital, not even family here, let alone war. But at the end of the 22nd century, a sudden air crash broke this rare peace, and the world continued to suffer disasters. A few years later, a large number of mutant beasts suddenly appeared all over the world. They are destroying the world wantonly, putting the civilization that has finally developed into an existential crisis again. Later, under the decision of the General Administration of Humanity, an elite team named "Yi" was formed. He was secretly sent around the world to investigate the truth behind the cause of the disaster. Is it really just a natural phenomenon behind all this? If this is the case, what is the explanation for those cases that either disappeared out of thin air or died with bloodshed before their eyes?