This is the first time that Sumo becomes the social game. Besides, it is an official license title of Japan Sumo association.
Every sport became the social game in Japan. However, sumo is a ceremony as well as sports, and it have severe religious precepts, authority and a tradition. Therefore it was difficult to make it a social game like other sports willingly.
However, the sumo has already become the trading card in a real life and card social games are very popular in Japan.
BBM 2012 大相撲カード BOX
The sumo social game of GREE is developed based on this. In the game, users can build their own sumo stable(Sumo Beya: 相撲部屋), train wrestlers and fight wrestlers from other users. All wrestlers appearing in the game are real life sumo stars.