The Guide is Actually a Body-Switching Esper [BL] - Chapter 259: Dark Locked Room

The end of all worlds approaches.

The Demon King Order harvests lives from all manners of living beings.

Within this darkness full of despair,
A single person escaped from space-time, returned to before the world collapsed, determined to change the fate of the past.

But as time pass, he gradually finds out that the Apocalypse isn’t quite as simple as he thinks…

- Description from novelupdates

Skyler's story was typical. He was publicly labeled a waste with no future as a Light — awakened individuals capable of wielding elemental powers. He thought that would be the end of it. But no, apparently that was not the case.He was teleported to the 'Battle Royal' to fight, even though he had zero powers and his age and potential were 100% ineligible!To make matters worse, he was not even the protagonist or transmigrator! He was just a freaking side character destined to die young in the story! And his death served only one purpose — to bring his sister closer to the protagonist!What a pitiful ending, right?However, unbeknownst to all, he wasn't meant to die but to become the best in two other realms, and they had altered the fate of that powerful King. Yet, there was a tiny problem — he didn't remember how he became overpowered in his past.