Fujita Seiko was supposedly the last soke of Koga ryu ninjutsu, and he died in 1966 leaving no heir. Any other sources that have surfaced which I have seen are laughable at best. We don't even practice much "ninjutsu" in the Bujinkan, so I have no idea what Koga ryu is supposed to be composed of, technique wise.
There is an interesting article on the history of Koga ninjutsu here:
http://www.bujinkanwakodojo.com/bwd_...u_history.html
Sorry I can't give much of an answer on this one
