Floyd Mayweather Jr. announced Monday in Tokyo that he has agreed to a bout in the Rizin Fighting Federation.
Mayweather will fight on Dec. 31 at Saitama Super Arena in Saitama, Japan.
Both Mayweather and his opponent, Tenshin Nasukawa, were introduced at a news conference in Tokyo by Rizin officials.
"It wasn't easy to make this happen," Mayweather said, "but we told the people anything is possible, so now we're here and we wanna make sure that we give the people in Tokyo what they wanna see -- blood, sweat and tears."
It was not clear whether it will be a boxing match, an MMA fight or some other combat sport. The promoters said they were still working on the specific rule set.
Prior to the announcement, Mayweather posted a photo on Instagram of himself wearing Rizin gloves with the caption, "December 31st 2018 #Tokyo"
Nasukawa is an undefeated 20-year-old who recently beat former UFC fighter Kyoji Horiguchi in a kickboxing match.
"I'm older now," Mayweather said. "I think that when it comes to experience, I have more experience on my side. But when it comes to youth, youth is on his side."
Information from ESPN's Ariel Helwani was used in this report.