"Yin Yang"
I'm getting the feeling that rather than harem (which I hope is no longer a ridiculously banned word when its a tag) its more of a booty call setup where he's just one of the guys having fun with them when he and them are around.
Which is not a harem and no bueno.
so let me understand this, this is mc's cheat? a book with s*x positions? does this book also have other jutsus that help mc keep the girl loyal to him or bound her to him so she wont go away once he start the harem? or he is going to recreate or boost those jutsus in that book somehow? :/