'Utano Hiro,' who worked at a research institute, suddenly gets caught up in a strange phenomenon one day. When he wakes up, he finds himself in a desolate, apocalyptic world filled with horrifying "aberrant beings"! The weapon Hiro obtains is a mysterious gun called 'ES707,' which has the ability to turn back time. To reunite with his beloved partner, 'Emma,' Hiro sets out on a journey to travel back in time using this gun! Encountering various survivors in the post-apocalyptic world, repeatedly turning back time, and facing relentless battles, Hiro gradually uncovers the mysteries of this ruined world... What exactly happened to the world? Can 'Hiro' safely reach the origin of everything, 'DAY 0'?!