Shinka no Mi - Chapter 173: Night Ruler*

Humanity had finally ended the war with the Demon Race and sealed them away, forever.However, they now have to face the treat of the Shadow World, an equally dangerous threat to their civilisation under the rule of the Emperor!Facing only misfortune from a young age, Nikolaus Reinhardt never expected anything good to happen to him.But his world completely changed when he awakened as an Ascendant, and accidentally summoned a member of the Demon Race in his house.Just because he messed around with a god damn book!

When the spiritual barrier that has been intact for a hundred years is shattered by a meteor, spiritual energy that had disappeared starts to return.The mystical realm slowly begins its revival—magic, witchcraft, curses, supernatural lifeforms, strange and mysterious legends, monsters and gods from other worlds…The old world order collapses, yet the new order is mystifying and chaotic.Just before the unprecedented reformation is here, Tang Qi awakens and finds himself hung on the cross, having turned into an inferior demon and in great pain and agony…With his special ability to see through the nature of all things from the mystical realm and a sly and crafty mind, follow Tang Qi as he develops new skills and powers—as well as making new friends and allies—to battle and protect himself from never before seen supernatural threats in an unfamiliar world!

To save a doomed fantasy world, I killed the main characters, then destroyed the game world, and fell into another timeline as the academy's top seat and rival to the protagonist.Now, I'm trying to save the world and steer it towards a better ending…But I'm the final boss.