TOKYO — “Suspect X,” a mystery starring TV heartthrob Masaharu Fukuyama and Kou Shibasaki (“Dororo,” “Shaolin Girl”), opened atop the Japanese B.O. for the weekend of Oct. 4-5.The pic, which bowed on 410 screens, had the seventh-biggest opening weekend for a Japanese pic this year, with $5.28 million. Distrib Toho predicts a final total of $38.8 million. The pic is helmed by Hiroshi Nishitani, whose credits include the 2006 Fuji TV hit “Star Reformer.” Produced by Fuji TV, “Suspect X” is based on hit series “Galileo,” which preemed on the net in October 2007. The show was, in turn, based on a bestselling mystery series penned by Keigo Higashino. To boost the pic, Fuji aired a “Galileo” special on Oct. 4 that scored a strong 20.8 rating.