Back Wine has been produced in Japan for centuries, and it was during the Edo period that the local white grape variety, Koshu, first appeared. The vineyards are mainly located south-west of Tokyo, in the Mount Fuji wine-growing region. Koshu is of course produced there, although it is gradually facing competition from international grape varieties such as Merlot and Chardonnay. Numerous trials are currently being conducted to cross Koshu with different Western varieties. White Kai is obtained by crossing it with Pinot Blanc, while Black Kai is the result of a cross with Cabernet Sauvignon.