Manny Pacquiao signed a mystery contract earlier this week with the fledgling Japanese mixed martial arts firm Rizin.

Rizin is the events organizer that promoted Floyd Mayweather's bizarre one round knockout win over the up-and-coming kickboxer Tenshin Nasukawa.

Pacquiao will be at an upcoming show in Yokohama to lend his support to a Filipino fighter who is challenging Nasukawa to a kickboxing fight.

Rizin executives are reportedly eager to commit Pacquiao to an actual fight in the future, and want to match him against an experienced martial artist called Takanori Gomi.

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We're learning more about Manny Pacquiao's deal with Rizin, just days after the eight-weight world champion boxer signed a mystery contract with the the Japanese mixed martial arts firm earlier this week.

A fledgling combat sports events organizer founded in 2015, Rizin piqued the interest of the global media when it promoted separate fights involving elite fighters like the decorated heavyweight Fedor Emelianenko, the 6-foot-2 jiujitsu expert Gabrielle Garcia, and the retired unbeaten boxer Floyd Mayweather.

Now Rizin is hoping to keep its name in the media by luring Pacquiao to Rizin 15, an upcoming festival of fights on April 21 at the Yokohama Arena in Yokohama, Japan.

Rizin CEO Nobuyuki Sakakibara confirmed the news on Sunday when he tweeted that Pacquiao is following Mayweather into the company. "Following Mayweather, Rizin 15 will make a new gimmick with this guy," he said, in a tweet supported by two photographs which appeared to show Pacquiao signing a contract.

Now, we're learning what Pacquiao's contract which actually involve.

Here are the most important points:

Pacquiao will be at Rizin 15 to support a Filipino fighter. The fighter, Fritz Aldin Biagtan, is challenging Mayweather's former opponent Tenshin Nasukawa. The bout will use kickboxing rules and will be fought at a catchweight of 59 kilograms. Pacquiao will not be fighting at all at Rizin 15. Nobuyuki could be looking to tie Pacquiao down to a further contract that could see him fight an experienced mixed martial artist called Takanori Gomi in the future.

Rizin's current deal with Pacquiao does not include a fight — boxing rules or otherwise. "This is not a fight contract," Sakakibara said, according to MMAFighting.com. "This agreement was made based off of Manny Pacquiao supporting the young Filipino fighter who will be fighting Tenshin Nasukawa."

Nobuyuki Sakakibara (middle) with Floyd Mayweather and Tenshin Nasukawa. YouTube / RIZIN FIGHTING FEDERATION Official

MMAFighting reports that the deal was struck with the view that Pacquiao's support for the Filipino fighters on its roster will see those athletes get bigger opportunities in the near future.

Read more: Floyd Mayweather's fight against Tenshin Nasukawa was fake, former UFC heavyweight says

With Pacquiao and Rizin executives in Yokohama this month, a second contract could be discussed as Sakakibara is eager to match the veteran fighter against Takanori Gomi, the iconic Japanese martial artist who engaged Nick Diaz in an all-time classic fight at Pride 33 in 2007.

Gomi, a former Pride lightweight champion, has since challenged for regional titles and remains an active fighter in the Rizin organization. Gomi most recently competed at Rizin 11 when he knocked out Melvin Guillard in the first round of a Saitama show in July last year.

Pacquiao, meanwhile, is enjoying a late career surge as the 40-year-old rolled back the years to demolish Adrien Broner on points in January, six months after stopping Lucas Matthysse in Malaysia.