Undefeated boxer Floyd Mayweather Jr. returned to retirement after defeated mixed martial arts superstar Conor McGregor inside the squared circle. However, since then, "Money" Mayweather has since returned from retirement to announce his MMA debut. Floyd Mayweather Jr. is now set to face Tenshin Nasukawa under Rizin Fighting Federation on Dec. 31. The bout will be under "special rules." However, the details concerning the rule set for the mixed martial arts match up have yet to be revealed. Tenshin Nasukawa has since come forward to offer his thoughts on the upcoming event. Taking to Instagram, the fighter offered the following message. "I\u2019ll absolutely win. Cuz I born to change the world with this fist. Who\u2019s gonna fight together with me as Team Tenshin? See you at RIZIN. #TeamTenshin #Cygames #RIZIN14 #mayweathertenshin #challenge" https:\/\/www.instagram.com\/p\/Bpzj1M8lI_3\/ Tenshin Nasukawa is a decorated kickboxer and a budding mixed martial artist. Fighting out of Tokyo, Japan, Nasukawa is the reigning RISE kickboxing featherweight world champion. As an kickboxer, Nasukawa has amassed an impressive 27-0 record. Meanwhile, the fighter has earned an undefeated record of 4-0 as a mixed martial artist. Check out a video of some of Nasuwaka's previous performances within the video provided above. For more MMA news click here.