Gates open up around the world, main character was the last hero of humanity to live. He tries to stop his old friend from completing a ritual of a time cult, ends up failing, even though he thinks he succeeds and goes back in time with his ‘friend’ when he dies killing a monster from a gate. His ‘friend’ doesn’t know he travelled back in time. And he also can go into one of the 72 demon lords body every once in a while, and is trying to defend earth from both within and without.