The game takes place in 2015, and the parasites were first encountered in 2011. If so, how could a man, who is clearly in his twentys and has lived a relatively normal life (for a ninja) have been genetically modified with toxic blood for the express purpose of being immune to something that had yet to be discovered at that time of his birth? Not to mention the fact that apparently his father also has toxic blood, and is in his fifties at least!
Also the fact that the Slime Chopper might not actually be possessed, all that organic mass may actually be the heavily mutated pilot!!
