This is absolutely just a rumor at this point, but it's a big enough one that it is worth running...
Reports out of Japan are indicating that on New Year's Eve, Kid Yamamoto will be facing K-1 MAX legend Masato under K-1 rules. Surprisingly, this fight is not linked to the Fedor Emelianenko-led Rizin event, but would be a rival to Rizin.
For fans who did not follow the Japanese combat sports scene back in the glory days of Pride, K-1, etc, it's hard to emphasize the magnitude of this fight. Yamamoto and Masato were two massive stars in Japan with huge followings. Yamamoto was one of the featured fighters on 5 different New Year's Eve mega-shows, as was Masato. In 2004, the two fought on the K-1 Dynamite!! show under K-1 rules, with Masato claiming the decision win. A rematch between the two would draw very big numbers from Japanese audiences, no doubt.
Masato retired on New Year's Eve 2009 as the #1 Lightweight in all of kickboxing. Yamamoto has been fighting in the UFC in recent years, returning earlier this year after a 3 year layoff. It is unclear at this point if the UFC is allowing Yamamoto to fight, or if he is no longer under contract.
With Fedor on one channel and Masato vs. Yamamoto on another, it looks like this New Year's Eve in Japan might be the kind of night their combat sports scene has not seen in many years. Let's see how it all plays out.