Shinobi: Shadow Beasts

Have you heard about the Shadow Beasts? Some people say they are creatures made of negative chakra, some say they are the opposite of the Bijuu.
But, the truth?
They are special creatures that shouldn't exist in this world, creatures that appeared because of a minor character that shouldn't exist in this world and that have the only mission of stopping them.
That's the story of Daniel- I mean, Shikamaru Kurai, as he is known in this new life.