"You're the air I'd kill to breathe again." Just like that, she escaped death's grasp: she's alive, but not quite the same. In the past, Nayeon would've really liked the idea of just being a warm body next to Ivory but both of their bad decisions had led them into a present that could not create that possibility anymore, leaving them the only impossible option: go back to the past and fix their lives which would eventually lead to multiple disasters. While challenging the consequences of meddling with time and physics, humanity learns the secrets of the Earth through distant relatives from the Intergalactic Union.