The Kinoshita Group Japan Open Tennis Championships is the longest-running ATP Tour tournament in Asia, first held in 1972. The ATP 500 event is played at the Ariake Colosseum, an expansive tennis centre comprising 48 courts and a stadium with one of the first retractable roofs in tennis. Japan's Kei Nishikori won the 2012 and 2014 titles.
https://www.atptour.com/en/tournaments/tokyo/329/overview