The omnipotent sage

I think it's just not a very good translation.
The book title is 《青帝yu女经》which Systran translates as "Jade Emperor's Yu's Daughter Sutra".

Likewise, the translation in the sentence below appears to be missing at least one word that would have been helpful. (in bold):
  Although he had often enjoyed such Japanese specialties films in his former life, in this life he was too young, only eight or nine years. He feared this kind of book could turn him into a psycho"

In addition, the phrase "this kind of book could turn him into a psycho",  Systran suggests "reading such books can be perverted".

So basically, it's just a fictitious book of the 'adult' or 'perverted' type that he is too young for. 

I can only find about Jade Emperor who is the highest deity of Heaven. He had a daughter that fell in love with a mortal.

Other is Candi, the Green Emperor aka the Green Deity aka Great Deity of the Eastern Peak ( Mount Tai ).

Maybe it's a forbidden book during ancient time? I do not know any forbidden books so I can't help you with it. Or it's just any ordinary in-universe treasure. 

Ok so i looked at the raw text. Usually when you see a random pinyin in text, that indicates that it has a sexy/mature context, in this case “yu” probably means “with” (yu could also mean "desire", the author is probably going for the double meaning here too)

Qing di = green emporer =  person from chinese creation mythology = fu xi (this is the real name)/dong fang tian di(great deity of the eastern peak above prob came from this)/ dude with way too many titles and names
*Note. Green emporer DOES NOT equal Jade emporer. Those are two very differrnt people

Nv Jing = the girl is 99.9% Nu Wa = Fu Xi's wife & sister (yea...) shes a very important goddess anyway...
Nv Jing was used as a x rated book title from ancient china( more complicated than this but the basic idea is this)

Thus the implied title = Fu Xi and Nv Wa's xxx chronicle. A more accurate title that would make some sense for english readers without the cultural background = The Green Emporer and his wife's "Story"