There's two fighter corners on the arena: Byakko (White Tiger) side and Seiryu (Blue Dragon) side. The people gathering in the arena are selected through special routes to maintain absolute secrety.
During the summer "Siege of Osaka" (1615), the Toyotomi Clan fell to ruin. But there was a lots of masters of fighting who only saw the battlefields as a places to express oneselves and they treated it as merely the coming of winter. The inevitable result was an increase of bloody incidents all over the country. Worried about the chaos and the public order, the shogun of that time, Iemitsu Tokugawa, in order to take hold of the fighters' place of self-expression, made the decision to create an arena. He ordered this to his most trusted friend - Mitsukuni, child of Yorifusa Tokugawa. Mitsukuni, also known as Mito Kōmon, had a villa at Kouraku, Bunkyo, Tokyo. In other words, he created the arena in that place.
But in 22 year of Meiji Era (1889), the duels became outlawed. Then Mitsunobu Tokugawa, with the interest of upholding public order, established a tolerable alternative. And according to Mitsunari Tokugawa (his son) words, even if Mitsunobu was eventually assassinated, he wouldn't let it fall.
Later, construction on the Tokyo Dome stadium began on the 5th month and 60th year of the Showa Era (May, 1985). At that time, in exchange for financing of the construction costs, a single financer, Mitsunari Tokugawa, made a deal to have his own private room in the Tokyo Dome. Everyone thinks the stadium have six stories above ground and two stories below ground, but the truth is that there's six stories below ground. At the very bottom there's the Underground Arena and Mitsunari Tokugawa is the owner of the arena. The Tokyo Dome also is located at Kouraku, Bunkyo, Tokyo.