The Ethiopian is also bidding to become the first woman to defend the crown after beating Helah Kiprop and Tiki Gelana last year.
But the 22-year-old is targeting the Games later this year.
"In order to make the Ethiopian Olympic marathon team, I must win the Tokyo Marathon on Sunday," Dibaba said.
"Of course, the time is also important, but if I win on Sunday, I have a chance to make the team
"All the runners are quite strong, but I want to make good effort to win."
In the men's, Dickson Chumba has a chance to join Eliud Kipchoge atop the World Marathon Majors series if he wins.
The Kenyan is equal second in the standings on 34 points, 16 adrift of Kipchoge – who is not in action.