Everything we know so far about Floyd Mayweather's extraordinary move to MMA firm Rizin, where he'll fight Tenshin Nasukawa in Japan

YouTube / RIZIN FIGHTING FEDERATION Official

Rizin press conference.

• Floyd Mayweather has announced his comeback.
• The American boxer, unbeaten in 50 professional bouts, has struck a deal with the mixed martial arts firm Rizin.
• Mayweather will compete against a fighter half his age, the undefeated kickboxer and mixed martial artist Tenshin Nasukawa.
• The show takes place at the 37,000-capacity Saitama Super Arena in Saitama, Japan on December 31.
• Here's everything you need to know.

Floyd Mayweather is coming out of retirement to fight once again.

The American boxer, unbeaten in 50 professional bouts, has been linked with a rematch against Manny Pacquiao as well as a boxing rules contest against the UFC lightweight champion Khabib Nurmagomedov in Russia.

But Mayweather stunned the fight game by attending a press conference on Sunday where it was announced he will fight 20-year-old kickboxer Tenshin Nasukawa at Rizin 14.

Here's everything you need to know about Tenshin Nasukawa, Rizin, and the shock fight scheduled to take place at the 37,000-capacity Saitama Super Arena in Saitama, Japan on December 31.

I know the UFC, but what is Rizin?

Rizin Fighting Federation is a young mixed martial arts firm in Japan. It was set up by Nobuyuki Sakakibara, the former president of Pride Fighting Championship in 2015, and has organised 15 shows to date.

Rizin has focused on "Grand Prix" events where athletes are drawn into a knockout-style bracket, where the winner stays on to compete in another fight, sometimes on the same night, until a last-man standing - the grand prix winner - is eventually declared.

However, a lot of shows follow the more traditional format of a set number of individual fights, fought between two combatants. Its next show, called "Rizin 14 - Saitama," is one of those events - and Mayweather will headline it.

Prominent Rizin athletes includes the Brazillian jiu-jitsu hall-of-fame member Gabrielle Garcia, the former DREAM and ONE lightweight champion Shinya Aoki, and the former PRIDE heavyweight king Fedor Emilianenko, considered the greatest heavyweight in mixed martial arts history.

But a show featuring Mayweather tops anything Rizin has ever accomplished before - not least because they have managed to lure the unbeaten prizefighter to Japan, but because they now have a show that will be watched around the world, on one of the biggest fight nights in Asia.

Fight promoter Sakakibara confirmed the event on Twitter. He said: "Imagine these two fighting each other on NYE in the RIZIN ring!"

Tickets for the Saitama show on New Year's Even will range between $70 and $250 and will be "sold out fast," according to Bruno Massami, the MMA news editor of the Brazilian media company Gazeta Esportiva.

Who is Tenshin Nasukawa and is he any good?

Tenshin Nasukawa was not even born when Floyd Mayweather made his debut as a professional boxer in 1996. Nasukawa, born two years later in 1998, is 20 years old and half the age of Mayweather, who turns 42 in February 2019.

Despite Nasukawa's age, he remains one of the best up-and-coming talents in Asian mixed martial arts. He fought 104 amateur fights by the age of 18, winning an incredible 99 times. As a pro, he has entered 27 kickboxing bouts, winning all, 20 of them by knockout. He has also won every single one of his four mixed martial arts fights.

Nasukawa, just like Mayweather, is used to winning. But that's not all. "He's young, very strong, very fast, and he's undefeated," Mayweather said, according to MMAFighting.com. "It's obvious he's doing something right to be where he's at. So I'm proud of him."

On being offered a fight against Mayweather, the BBC reports that Nasukawa was surprised. "It was a surprise offer but I accepted without hesitation. It's the biggest moment in my life and I want to be the man who changes history. I'll do that with these fists, with one punch… just watch."

Will the fight be MMA rules or boxing rules?

Right now, that is unclear.

What is clear is that there is a very noticeable height and weight difference between the 5-foot-8 Mayweather, who tends to compete around the 147-pound to 154-pound weight category, and 5-foot-5 Nasukawa, who last fought in the flyweight (57kg/125 pound) division as recently as September 30.

"As far as the rule set and the weight and the rules, we still have some work cut out for us," Rizin boss Sakikibara said, according to MMAJunkie.com. "But it will be a great fight that everybody will be so excited to see. I'm so happy that Mr. Nasukawa accepted this offer in a flash."

The BBC also reported that according to Mayweather, the weight division and the rules and regulations would all be discussed "within the next couple of weeks."

However, John Morgan, the lead reporter for MMAJunkie.com, tweeted that the fight could be restricted to "three, three-minute rounds."

Morgan said: "Pure hearsay at this point, but I was told from a reliable source that the current plan for Mayweather on NYE isn't MMA, but specific rules not known yet. However, it would be an exhibition of three three-minute rounds."

Massami, meanwhile, expects a "standup bout with kicks."

A variation of a kickboxing bout could be what materialises, as Mayweather himself said the bout is "special" and he would be "giving the people something they've never seen before," according to a statement via Kevin Iole on Yahoo Sports.

Should I care about this fight?

Photo by Al Bello/Getty Images

Floyd Mayweather.

Probably.

If it's an actual fight, it could be interesting. Mayweather, boxing's biggest ever pay-per-view attraction, has never ventured outside of his sport, so if the rules include one kick, let alone all permitted kicks in kickboxing, then Mayweather enters unchartered territory against an undefeated Japanese fighter, in Japan, who is half his age.

But there are many unknowns. If ever you read the words "exhibition fight" then you can safely presume that means "glorified spar" - which is not worth a box office fee.

And Iole believes it could be even weirder than an exhibition fight. "We don't know if it's a real fight or something scripted like pro wrestling," he said.

Regardless, Mayweather has made a cameo appearance at a pro wrestling event before when he found a way to "win" against the Big Show, a huge man who is 16 inches taller than he is, at WrestleMania XXIV in 2008.

That event still generated over one million PPV buys.

No matter what the rules of this fight are, or if this is even a fight at all, one thing is for sure - Mayweather will make money and will be headline news the next day.

How much money will Mayweather earn?

Mayweather, as he will tell you himself, is a billionaire and became boxing's first billion-dollar fighter, according to Forbes.

It is therefore unlikely that Mayweather would get out of bed, let alone fight, for a considerable sum of money.

"Bank on this: Mayweather is going to be paid, and handsomely," Iole said on Yahoo Sports. "No one said how much Mayweather will make, but you can bet he wouldn't have taken the bout had he not been guaranteed a nine-figure paycheck."

What this means is simple. Mayweather could be looking at another $100 million paycheck.