Complex sentence: The current most regularly used rule set--the one that is used on the international tournament stage--originated in Mito, Ibaraki, Japan in the 1970s: the Japanese game company Tsukuda Original registered the game under the trademark name "Othello".
Split into simpler sentences: The current most regularly used ruleset--the one used on the international tournament stage--originated in Mito, Ibaraki, Japan in the 1970s. The Japanese game company Tsukuda Original registered the game under the trademark name "Othello".