The Naruto characters can fit into the Crysis world in fanfiction in many ways. Take Rock Lee, for example. His taijutsu skills would be very useful in close - quarters combat in Crysis. He could use his speed and powerful kicks and punches against the soldiers or alien creatures in Crysis. Also, the concept of chakra in Naruto could be related to the energy sources in Crysis. Maybe the characters find a way to convert chakra into a form that can power up the technology in Crysis, creating a unique blend of their two worlds.