On K-1's English site there was an in-depth article posted today by Stuart Tonkin entitled, Slay Or Be Slain - The Heavyweight Champion, that documents the history behind the K-1 Yokohama events. It's a pretty good read, here's a small snippet:

Since 2007 the first locally held K-1 event of the year has traditionally been held in Yokohama Arena. Thankfully, this year there will be no changes to what has somehow become a simple, yet magical formula to events a level of which is rarely seen.

Many of the jaw-dropping bouts of the past 4 years have taken place at this event. In 2007, among several other surprises, Mighty Mo did the unthinkable when he landed his "M-over hand"-right to ruin Hong-man Choi's night. And fan-favorite Ray Sefo dropped reining Champion Semmy Schilt for the first time ever in K-1, only to then be stopped by Hightower, also for the first time in K-1.

In 2008 Mark Hunt's long awaited return hit its' first bump when Semmy planted a spinning back kick into the Samoan's ample gut. Badr Hari came out with fire in his eyes and defeated Sefo inside of 1 round. And the Kyokushin star, Ewerton Teixeira made his successful debut.

Last year we saw Tyrone Spong's first appearance in a Japanese K-1 event, albeit an unsuccessful one. Ichigeki stable-mates Glaube Feitosa and Ewerton defeated their respective opponents. Peter Aerts beat young gun Errol Zimmermann. And, Remy Bonjasky defended the honor of K-1 fighters around the world by beating Alistair Overeem; dropping him in the process.

The common theme is that these Yokohama events rival even the WGP for the level of excitement, and there has been a wicked upset or two on each and every card thus far. What is more surprising is that there is just a single team responsible for each and every one of the upset-of-the-night fights.

You can checkout the full article here.