TOKYO — Warner Bros. is to exit the Japanese exhibition biz after 20 years in the country, following a deal to sell its stake in pioneering multiplex operator Warner Mycal.Retail group Aeon and WB have a 50-50 share in the chain, but Aeon is to buy WB’s stake. The acquisition will be completed by March. The value of the stock purchase was not revealed. Aeon will become Japan’s top exhibitor by combining Warner Mycal sites with ones it already operates through another subsid for a total of nearly 600 screens. Currently managing 496 screens at 60 sites across Japan, Warner Mycal is the country’s number two plex operator. WB has reportedly been considering ankling from the Japanese exhibition biz for the past several years. Overbuilding in certain markets has led to cutthroat competition and less revenue for operators. Annual per screen revenue now averages $640,000, down nearly 40% from 1993, when Warner Mycal launched Japan’s first true multiplex in a Yokohama suburb.