My Master Is Super Powerful But Overly Steady - Chapter 83

Hanjun, who used to live alone, wakes up in a strange, old church in a different world called Eorera. In this world, there are two gods: the God of Light and the God of Darkness. A thousand years ago, the God of Darkness created demons and attacked humans. The God of Light was nowhere to be found, and people believed they were abandoned.Hanjun finds himself mistaken for being the God of Light by an old priest who was praying for help against the demons. Even though Hanjun is not actually a god, he ends up in a divine body on a stone throne, realizing he has lost most of his powers. He decides to help the humans by recruiting players from Earth through a game he creates called “God's Games Online.”He sends out gaming equipment for free to a few selected players, who will enter the game to help protect Ulon Town from the approaching demons. Hanjun also creates a game system and an NPC guide, using the old priest named Barry to lead the players.Hanjun hides his true identity As “Holy Son” and starts preparing to gather faith and regain his power to protect the people of Eorera.

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates

In an era when the power of Fire Magic was considered to have reached its limit, one girl began researching nuclear fusion.

Kai of the Sorcerer’s Tower is one of the last mages left, barely surviving in a world ruled by creatures of the dark — where the era of mages ended, and most of the lands got contaminated with dead mana. To save his world and fulfil his master’s last wish, he put himself through a forbidden ritual, risking his soul being ripped into pieces to make his way into the past. In an era with abundant mana — an era yet to enter the Golden Era of Magic. Things go wrong, of course, as they always do, and he finds himself thousands of years before the world fell to mana contamination — in the body of a young lord, Arzan. All is not well, though, as the young lord was murdered by someone right at the cusp of a beast wave threatening the territory, while larger threats loom on the horizon. There was a lot to do for Kai to regain his former strength in this time of primitive technology, but then again, he might just be able to change that.