Tonfun is the 10th opponent in the game is often considered the toughest to defeat consistently. There may not be a 100% effecient strategy to beat him, but there are tricks that come close enough to it. Setting him up is the trickiest part to beating him.
Tonfun is possibly a more faster and agile version of Pole. He will scurry back and forth and pop you in the head with his Tonfun at his leisure. The best way I have found to take him down is to start the fight out crouching and waiting for him to get close. Once he is near jump to the right side of the screen, Tonfun will back up the same direction once you do. As you land quickly hit a Low Kick attack then immediately jump to the left side of the screen. The kick may hit or miss, but that's why you jump to the left and he will follow you again as you try to hit a Low kick again. Immediately jump to the right and repeat this method. It's really all about how you time your initial jump in the beginning because if done properly the kick will connect everytime and you may even Perfect him. Obviously setting Tonfun up is the hardest part to defeating him.