Mayweather will pocket tens of millions of dollars for the money-spinning event in Saitama, Japan, on New Year's Eve, but the rules are yet to be decided on a fight that could see Money's first departure from traditional boxing, The Independent reported.
Speaking at a news conference in Tokyo on Monday, Mayweather said the decision to fight in Japan was about expanding his global profile.
"I wanted to do something different. I wanted to display my skills outside the US and be in a special fight," he said after signing a deal with Japanese mixed martial arts promotions company RIZIN Fighting Federation.
"I spoke with my team and with RIZIN and we put it together. I have fought in the US for all 50 of my fights. As a professional I haven't had a chance to go outside the US to display my skills and to display my talent for the world."
Nasukawa competes in their championships in both MMA and pure kickboxing. He has won all four of his MMA fights.
While boxing rules restrict bouts to the use of fists, MMA rules can incorporate kicks, knees and elbow strikes, as well as wrestling, joint locks and chokes.
Mayweather said the terms of the fight would be decided in the coming weeks.
"As far as the weight class and the rules, we will talk about that and will get that situated within the next couple of weeks," Mayweather added.
The 41-year-old had earlier said he would be comfortable fighting under any format.
The RIZIN Fighting Federation was founded in 2015 by Japanese businessman Nobuyuki Sakakibara, who was previously the president of Pride Fighting Championships before it was sold to the then-owners of Ultimate Fighting Championship in 2007.
Sakakibara was clearly delighted with his coup.
"There were many twists and turns to get here," he said, sitting between Mayweather and Nasukawa. "We first negotiated with Mayweather’s side to convince him to join RIZIN.
"(Then) Nasukawa Tenshin was the first guy we could think of, and the only guy we can think of (for this match)."
Mayweather's last bout was in 2017 when he beat Irish MMA fighter Conor McGregor, running his boxing record to 50-0 and earning close to $300 million.
Mayweather had come out of a near two-year retirement to fight McGregor and afterward said he was done with boxing.
"We do foolish things sometimes but I am not a dam fool. If I see an opportunity to make $300 million in 36 minutes why not," he said after that fight in Las Vegas.
"But this is the last one, you have my word on it."