I'm pretty sure the MC was the author of said book, but here are things I remember about the novel. It's set in a sci-fi, in an academy. The Main character looks into a mirror and sees he has no face because the person he was reincarnated as wasn't described in the novel. The MC was ranked average and when it comes to weapon selection he chose a pistol. Firearms aren't really useful so his choice is laughed at. I could be mixing up another book, but the main character eventually joins like an group where each member is a color, and he becomes the member with the codename black.
You go to this thread, Click edit in the title Instead of forgotten title, click resolved. Hope that helps!