"I wanted to do something different", said Mayweather.
'I spoke with my team and with RIZIN and we put it together. "I want to fight him again but I'll fight whoever I gotta fight to get back to him if that's not the case'".
'When it's all said and done, it's all about me going out there and displaying my skills against another skillful fighter.
His opponent, Nasukawa has fought in RIZIN championships in both MMA and pure kickboxing.
At present, there is vast amount of unknown details; Mayweather said the format, rules and weight category of the fight are still to be decided. UFC boss Dana White said last week that a fight between the two would have to be in the UFC, which is something Mayweather would probably never agree to.
Mayweather turns 42 in February and hasn't fought since his 10th-round technical knockout defeat of McGregor in August 2017.
'My opponent looks taller than he actually is and I think that comes from the aura that he has, but I think I can hit him, ' he said.
'This particular bout is a special bout as far as we're giving the people something they've never seen before'.
And he faces a potentially risky prospect in heralded kickboxer Nasukawa, who warned he has a punch that will "change history". I look forward to giving you guys entertainment come December 31.
"And I would like to be the man who makes history".
Prior to Monday's news conference, Mayweather gave a select number of media interviews over the weekend, but the identity of Rizin's marquee recruit for the Saitama event had been kept under wraps.
After fighting the first 27 of his professional bouts at the super featherweight limit of 130 pounds (58.97 kg), Mayweather moved up to lightweight (135 pounds/61.23 kg) in 2002. I can box a lot a bit.
"It's really all about the skills, it's not about the weight". "He's young, fast, [has] youth, undefeated like myself, and what the people want is excitement and that's why I chose Japan".