The Art of Destiny: The War Arts Saga, Book Two

Once there was a prophecy that a Chosen One would rise to defeat the Eternal Khan, an immortal god king. 

But the prophecy was wrong. 

Now Jian, the former chosen hero of prophecy, is just an ordinary young man trying to find his own way. But he may yet have an extraordinary destiny, because he joins forces with Taishi, his grumpy grandmaster who instructs him in the ways of her powerful family war art. Jian still has a long way to go before he can become her heir, so she recruits a band of elderly grandmasters who have come out of retirement to whip him into shape and help with this one last job.