Introduction：Xiao Chun, Da Long, Eileen, and Harley, four graduating college students, have arranged to go hiking and camping in the suburbs. The four of them were enjoying the pleasure of this outing comfortably, when a huge explosion in the distance shattered their passageA rare moment of youth. When the four of them returned to the small town, they realized that the whole world had become different. After narrowly avoiding the pursuit of extraterrestrial mechs time and time again, they arrived in the pastThe home of a university professor in Japan. Professor Du told them about the ins and outs of extraterrestrial invasion, and the four of them decided to fight against the brutal appearance of the mecha together with Professor Du. Meanwhile, another surviving human organization is located in aUnder the leadership of the governor, in order to seize resources, the four of them engaged in fierce struggles with Xiao Chun and others. Faced with human slaughter and large-scale invasion by extraterrestrial mecha, the four of them had to grow rapidly in order to defend themselvesFighting for human dignity. But they didn't realize that war will never stop