https://youtu.be/wKGKp4s7lZU

Just assign the LT button to the Crawl Cyclone (you can buy it from the Bunkado Antiques and train it a little).
I suggest train that move 1/2 days before the big match. I've trained it the day before in 2/3 "workout", and it was ok.
Use Y when he goes behind you, or when he wanna use some strong hits.
If you are lucky enough you can "bug" it and keep kick him when he's on the ground.

I'm not the strongest player but I usually find the smartest way to do something boring (even if before there is a long unskipable cutscene....grrr.)

So here we are, the spammest and easiest way to beat that "adorable monster" called Chai.