Nile's Links
Now that he's died and become a Shadow, he needs constant energy or he'll perish. He chose Adam because, despite the teenager's (supposed) age, he never seems to tire and is always traveling.
He usually rests deep inside Adam's being when the host is out hunting for prey and thus is completely unaware of the other's true form and nature.
Nile's living host, though unaware.
Can feel something constantly weighing him down and his energy depleting far quicker than originally.