The manga is about a guy who is reincarnated to another world of magic and swords. He was born to a noble family. This guys is like a Chuunibyou, and he tries to make a organization of shadow (I forgot the name because this was also the manga title). He picked a girl and a bunch to make an organization.
This guy likes to look like he's weak despite really OP and what I like is when he got duel with a girl, he uses mob technique to make him look weak, really weak.