One day at KFC's Aoyama branch, a foreigner went to buy some chicken at KFC and said "I'm having a party but because there is no turkey, I've come to get some fried chicken instead."
in 1974, KFC then started promoting the catchphrase "Christmas = Kentucky" and poured a load of yen into the marketing effort. The catchphrase soon caught on and together with the commercials on TV, the Japanese then started to consume a load of Chicken during the festive season.