Four players currently ranked inside the top 10 will compete in the September 17-25 event, including two-time Grand Slam winner Garbine Muguruza and fellow Spaniard and world number four Paula Badosa.
Japan's Osaka beat Russia's Anastasia Pavlyuchenkova in the 2019 final but the tournament was cancelled for the past two years because of coronavirus.
Osaka, a four-time major winner and former world number one, has slipped to 44 in the rankings and lost in the first round of the ATP/WTA Cincinnati Masters last week.
Former champion Karolina Pliskova of the Czech Republic also returns to Tokyo, while world number six Aryna Sabalenka of Belarus and Russia's world number 10 Daria Kasatkina make their tournament debuts.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)