Seirei Tsukai no Blade Dance - Volume 20, Final Chapter - Return to the Academy

Dying in a tragic accident Marcus Ferrous gets transferred to a fantasy world of monsters and magic, except when he arrives contrary to what he expected he is now level one and a ghost. Left with nothing on a strange new world, Marcus will struggle with everything he has on his journey to get stronger and uncover the secrets of his new world.

An unexpected discovery in Machu Picchu has transported a young professional thief from Earth to a world filled with mystical powers and evil plots. With his beloved teacher and best friend killed during the calamity, his only goal is to become stronger, so that he can take revenge for them.This is a novel filled with politics, the struggle for power, evil beauties, and of course, Divine Immortals.

- Description from Novelupdates

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

When I woke up after a pretty crappy death, what greeted me was one of those famous fantasy worlds! I didn’t expect anything like becoming the strongest with a common job, or rising to the top with the weakest class…