To Be a Power in the Shadows! (WN)

Just like how everyone adores heroes in their childhood, a certain boy adored those who hid in the shadows. One day, after living the mediocre life of a side character while undergoing frenzied training by night, he reincarnates in a different world and gains ultimate power. The young man who is only playing at being a secretive powerhouse, his misunderstanding subordinates, and a struggling, giant, shadowy organization…

This is the story of a boy who adored shadowy manipulations who might possibly reign over the dark side of another world.