AINU Of Japan.
Ainu and Polynesians are given as the closest affinity for Kennewick but the differences were enough not to place him in those groups.
“Using the principal component scores to generate inter-individual distances (Van Vark and Schaafsma 1991), the Kennewick individual is closest to south Pacific (Moriori, Easter Island) and the Ainu of Japan. The typicality probabilities for the PC reduced data, which are the least conservative estimates of group membership, all indicate that the Kennewick cranium is not morphologically similar to any modern human population (Table 7)” http://www.cr.nps.gov/archeology/kennewick/powell_rose.htm