Everyone Else is a Returnee

Synopsis

In a primary school excursion he was left behind alone. In a junior high school camp he was left behind alone. In a high school field trip he was left behind alone. In the end I became a uni student but so what? This time I was left behind from the entire human race! While everyone left this world I was the only one to protect Earth! A legend will start when the human race returns and a disaster strikes! (Source: MU)