"I always dreamed that I would play against Serena in a Grand Slam final," Osaka said.
The youngest player to reach a final at the US Open since 2009, Osaka showed balance and mental strength by saving the 13 break points she faced in a semifinal victory over American Madison Keys.
Her powerful running game has taken her to the final with the loss of just one set, her contagious enthusiasm for the peculiar challenges of the US Open has won her a legion of fans along the way.
"I like to sweat," Osaka said about the punishment and humidity that has put the biggest names on their knees.
And he will do it against Williams, who is in the same way looking for his first Grand Slam title since the birth of his daughter Olympia on September 1, 2017.
A year ago, at this time, Williams was in the middle of four postnatal surgeries.
After tantalizingly approaching Australia's Margaret Court record of 24 Grand Slam titles with a Wimbledon finalist, Williams says the milestone is not her primary focus.
"I'll keep trying," he said. "If it does not happen, I'll keep trying for the next one."
That's not the only record in Williams' sights Saturday.
With a seventh US Open title to go with those he won in 1999, 2002, 2008, 2012, 2013 and 2014, he can break a tie with Chris Evert by more than ever.
Williams says it's hard to gauge how close he is to his best dominant position, but there's no question that he's playing well above his 26th world ranking and even the 17th placement given by US Open officials.
She leads the tournament with 64 aces and has broken only six times in six games, while Osaka has dropped her serve only four times.
The numbers promise a brilliant combination, if the magnitude of the occasion is not too much for Japanese youth.
"I feel that although I should enjoy this moment, I should still think it's another game," he said. "I should not think of her as my idol, I should try to interpret her as an opponent."
Williams is not worried that his only previous meeting, in Miami in March, was a victory for Osaka.
"It was good to play with her because I know how she plays now," Williams said. "I mean, I was breastfeeding at that time, so it was a totally different situation.
"I have nothing to lose," added Williams, who can join the Australian court, Evonne Goolagong and Belgian Kim Clijsters as the only mothers to win a Grand Slam title. "I will go out and do what I can".
Meanwhile, Osaka will do everything in its power to bring the confrontation to the conclusion of his youthful dream.
"I do not dream of losing," he said.