I'm A Spider, So What? (WN) - Chapter s37.3: S37 Skirmish – Oni vs Wind and Lightning 3

He became a teacher at the best magic academy in the empire.
….For being mistaken for someone else.

Kim Jeongjin, an editor of a publishing company on the brink of closing due to bankruptcy, ends up transmigrating inside a fantasy novel as the incompetent youngest son of a wealthy family.

And here he thought that he should live a rich life in this life…

“Why was I given a high-level skill? Don’t even bother!”

“Kill Hamyuts Meseta”

A story about a world where all dead people become “Books” and are housed in a Library. The boy named Colio Tonies had his memories taken and a bomb transplanted in his chest. His life’s purpose is killing the world’s strongest Armed Librarian, Hamyuts Meseta. But, one day he gets his hands on the “Book” of a beautiful princess and falls in love at first sight. Furthermore, that love will cause Colio to get involved in a grand scale battle…

The formless ancient world was infested with despicable demons. They hunted and feasted on mankind, keeping the human civilization constantly in a weak and suppressed state.

During the first known year, a magical mountain descended into the world from the realm of the Gods. Carved on this enormous mountain was a message: ‘Heaven Prevails’…

After the Grand Descent, a name that was given to the descending of the mountain, the Three Great Sages made their ways to Mystic Mountain where they learned to harvest what we now call magic, establishing the Mystic Cults and eighty-one sacred shrines to help aid mankind with the cult’s mystic powers against the eternal fight to the death with demons.

- Description from Novelupdates