Idle Mage: Humanity's Strongest Backer - Chapter 16: Mystic Academy is where?

An RPG gamer who played the realistic VRMMORPG ‘The Amber Sword’ for years, finds himself teleported to a parallel world that resembled the game greatly. He takes on the body of an NPC who was fated to die, and with the feelings of the dying NPC and his own heartrending events in the game, he sets out to change the fate of a kingdom that was doomed to tragedy.

- Description from novelupdates

Mason was a mercenary, until the day he died on a mission after being betrayed by his unit.

Alex Walker was a living legend in the game. Some argue that he was the best midfielder in the world back in his prime... The same people would tell you flat out that he was the worst manager in the world.Three relegations in his first five years... erratic relationships with his players and tens of millions of money spent on unknown players with little to no identity.After suffering a heart-attack on the back of yet another relegation, Alex Walker wakes up to something strange.[Ding! Coaching system has been awakened!]

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates