Who finds it?

A certain Phenex

Curling up in his room after the humiliating defeat on the hands of a newly reincarnated devil, Riser Phenex was a truly pathetic sight. His pride was utterly crushed that day, his future bride stolen and everyone looked at him as if he was trash since that moment.

The day that should have been the most important in his life, the one that would let him be more than the spare of a spare for the house Phenex, all ruined because of some reincarnated devil.

KNOCK

"Big brother, you there?"The sweet voice of Ravel spoke from the other side of the door and Riser felt himself curling up even further, not wanting to meet her more than anyone else.

She was the one who always admired him in the family, the only one he felt was fully and completely on his side, and now she had seen him losing like that.

"Big brother, please come out. We are getting worried about you." Ravel said and Riser slowly took a breath before he walked out of bed, but not towards the door but towards a stand on the side where several books were located.

He would stay right here and just go read something to distract himself from him family and what has happened.

"Huh? Since when do we have this?" Riser said, pulling from his bookcase a simply black book with the title Rulebook.

Opening it up there were written down several regular rules of society in it, from stupidly obvious ones like 'Angels will fall if they have sex for lust' to really weird ones like 'Venelana Gremory likes worship sex'.

It was absurdly detailed, and Riser actually found it rather funny.

Deciding to mess around with it Riser took out a pen and decided to write something just for shits and giggles, a petty **** against Rias, her peerage, and especially the worm who humiliated him.