Hibiki Mamiya is a genuinely kind and optimistic young man, happily working as a car mechanic and sharing his life with his girlfriend, Kurumi Ogasawara – they’ve been together since high school. With marriage on his mind, Hibiki meticulously plans the perfect proposal. But just as he's about to pop the question, a sudden accident sends him plunging into a tunnel, leaving him trapped for four long days. When he finally emerges, however, it's not the world he left behind. The streets are eerily empty, traffic signals are dark and lifeless, and unsettling crimson stains mark the pavement. Where has everyone gone? Driven by worry, Hibiki sets out on a desperate search to find Kurumi and uncover the mystery of what happened to his town.