When Earth is invaded by demons in 3089, a hero named Altair steps up to stop them and save humanity. Armed with grafting technology that allows humans to use demonic powers, Altair bravely fights a demon army with record-level strength and defeats them before dying. But to his surprise, he wakes up 60 years later in the body of a weak cadet who coincidentally shares his name. Now Altair must whip himself into shape while keeping his massive demonic power under control so he can protect the world once more...!