Gambling on sumo, like most sports in Japan, is illegal.
The Japan Sumo Association also takes a tough line with any of its members involved in such activities, even kicking an ozeki (Kotomitsuki) and stablemaster (Otake) out of the sport completely in 2010 over their involvement in a baseball betting ring.
If there were books open on sumo, however, Kakuryu would have the shortest odds to emerge victorious in the upcoming Summer Grand Sumo Tournament.