Read Kage no Jitsuryokusha ni Naritakute Manga:
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, hi more.. s 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.