Originally founded in 1915 under the name of the Japan International Championships, the Japan Open is a men's ATP 500 tennis tournament held at Tokyo's Ariake Tennis Park. The hard court event is organized by the Japan Tennis Association and currently sponsored by Rakuten, and brings some of the biggest names in the tennis world to the city.
Tickets for the event typically go on sale during July and August, so it's advisable to keep an eye on the official event website during that period for information on how to secure a seat.
General sales have opened up, which can be organized via Lawson stores and a couple of other places.