Hiru wa Betsu no Kao

After graduating from school, the main character starts to operate an underground Internet site. One day he is offered a Jewish book dating from 1000 years ago. He buys the book and tries to translate it. It suggests to search for naughtiness. It looks ridiculous, but everyday life changes little by little. He starts to exchange emails with four women to learn their identities and train them.

[From vndbreview]