Infielder Kazuma Okamoto and pitcher Kona Takahashi are entering Major League Baseball’s posting system and will be available for teams to sign as free agents from Friday through Jan. 4. They join power-hitting corner infielder Munetaka Murakami, whose 45-day window to sign expires Dec. 22, and right-hander Tatsuya Imai, who can sign through Jan. 2. Okamoto hit .327 with 15 homers and 49 RBIs in 69 games this year for the Central League’s Yomiuri Giants. He injured his left elbow while trying to catch a throw at first base on May 6 when he collided with the Hanshin Tigers’ Takumu Nakano, an injury that sidelined Okamoto until Aug. 16.