Mahouka Koukou no Rettousei - Chapter 8Volume 23 -

Ambrose Lu possesses the Eternal Longevity Body, granting him immortality and eternal life.Throughout countless years, he has traveled through myriad worlds, gained infinite experiences, and held various roles.He has been a leisurely Immortal Emperor, a tavern keeper selling wine, the mysterious leader of a sect known as the Carefree Sect, and a divine healer saving lives in his medical clinic.Additionally, he wields blade as the Green-Clad Sword Immortal, using his sword aura to sweep across the world!

An ordinary student, a wretched peeper, a cowardly teenager with a kind heart. In a terrorist attack, he inherited the knowledge of countless elites, embarked on a path of God Jagged Tu…

He is an artist!

He is a mathematician!

He is a psychology Doctor!

He is a master of fighting!

In fact, he is a man

Taken off raw site:

A wretched, dirty young man is working during the summer when he was caught up in a mysterious explosion. After that explosion, the young man is then left with the memories and knowledge of dozens of the world’s experts.

He has changed, his heart has become cold, iron-blooded. He became a killing machine, his mind turned mechanical, calculative. Everything goes according to his plans and calculations!

In this magical, slaughterous world, a door is opened for him…

- Description from Novelupdates

Just like how everyone adored heroes in their childhood, a certain young man adored those powers hidden in shadows. After hiding his strength and living the mediocre life of a mob character by day while undergoing frenzied training by night, he finally reincarnates into a different world and gains ultimate power. The young man who is only playing at being a power in the shadows, his misunderstanding subordinates, and a giant organization in the shadows that gets trampled…. This is the story of a young boy who had adored powers in shadows possibly eventually reigning over the world of shadows in another world.

Waking up, Kim Hajin finds himself in a familiar world but an unfamiliar body.