Floyd Mayweather, at a press conference in Tokyo, announced on Sunday night that he will participate in a fight in the Rizin Fighting Federation on Dec. 31 at Saitama Super Arena in Saitama, Japan (about a half hour outside of Tokyo). It was not clear if 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. Mayweather and his opponent, Tenshin Nasukawa, both were introduced at the press conference by officials from the promotional company.