Kyle gets sent back 4 years to when demons first invaded, just before defeating the final boss. With his future knowledge and abilities, he aims to stop the disasters from happening again.
Kyle finds himself transported four years into the past to the beginning of the demon invasion, right as he was about to finish off the final boss. Armed with the memories and skills he gained in that time, he'll endeavor to prevent the same tragedies from occurring.—Crunchyroll News
