Mayweather's showdown with 20-year-old Nasukawa will take place at the Saitama Super Arena in Tokyo, Japan on the RIZIN 14 fight card.
While he announced his return to action, Mayweather said the rule set for the fight against Nasukawa hasn't been determined yet, although sources say there's very little chance he'll actually compete in mixed martial arts.
"It's always been a goal of mine to go outside the USA and go into another arena and display talent as a professional because I did it as an amateur". Rizin is a MMA fight federation based out of Japan. When it's all said and done, it's all about me going out there displaying my skills against another skilful fighter.
The rules of the fight are still being worked on, according to ESPN's Ariel Helwani.
"I would probably say that this is my biggest event in life", Nasukawa said.
"Rizin has done a phenomenal job with the fighters", Mayweather said.
Sakakibara was clearly delighted with his coup.
Mayweather's last bout was in 2017 when he beat Conor McGregor, running his boxing record to 50-0 and earning close to $300 million.
In Tenshin Nasukawa, Floyd Mayweather will face one of the most impressive strikers in combat sports history.
Rizin FF president Nobuyuki Sakakibara, speaking through a translator, echoed Mayweather's confidence: "As far as the rule set and the weight and the rules, we still have some work cut out for us".
'(Then) Nasukawa Tenshin was the first guy we could think of, and the only guy we can think of (for this match)'.
That victory improved his boxing record to a ideal 50-0 but the format or rules for his meeting with the baby-faced Nasukawa were not specified by the Japanese mixed martial arts promoters RIZIN.
'We do foolish things sometimes but I am not a dam fool. While the organizations were initially meant to co-exist independently with occasional crossover events, the UFC instead absorbed many of Pride's top fighters before folding the operation.