Three years have passed since the day Takeru suddenly awoke in a world not his own — a war-torn alternate reality in which mankind was locked in a decades-long struggle against the ruthless extraterrestrial invaders known as the BETA. In that time, he’s been through an awful lot — enlisting in the military, meeting parallel-universe versions of his old friends, and even falling in love. But unbeknownst to Takeru, he and his squadmates were being trained to participate in a top-secret UN plan known as Alternative IV — a last-ditch effort to take back the Earth via experimental technology. Unfortunately, however, development screeched to a halt when the project’s chief executive, Professor Kouzuki, hit a wall in her research, and the UN opted to scrap the project in favor of its successor: Alternative V. A tiny fraction of the population would abandon the Earth in the hopes of finding life anew in another star system. Takeru is one of the ones left behind, and dies in a hopeless war against the BETA.

But it seems that fate has bigger plans for Takeru, because he wakes up to find himself back in his childhood bedroom once again. Not in his own world, mind you — but back where he was three years prior. . This was no dream; this was a recurring nightmare. But then it hits him: this is a second chance. Perhaps he can use his knowledge to warn Professor Kouzuki, and together, they can somehow find a way to prevent Alternative V from ever being enacted. If he can change history, then maybe — just maybe — he’ll find the answers to all of his questions. Why has he gone back in time? Why isn’t Sumika here? And most importantly, what IS Alternative IV?