In 2025, a comet’s arrival triggers an alien invasion of Earth. Humanity develops androids as anti-alien weapons, but ultimately faces extinction. In the desolate future where humans are extinct, an android named Licht lives alone. A high school girl named Seina accidentally time-slips from the past into his world, and the two begin traveling together. Licht gains tremendous strength by leveling up through defeating aliens. As the two grow closer during their journey, they struggle to prevent humanity’s extinction. However, Seina realizes a troubling possibility: if they change the future, Licht might disappear.