When you enter Kamui go to the right of the Guardian Sapling. You will find the Kokari boy and his dog Ume. To the right of them is the third dojo. There is a big pile of snow close to it. If you power slash it enough times, an ice statue of Issun x1000 will appear. Destroy it with Inferno and go in the dojo then go back out. The pile of snow reappear. If you power slash it again, a statue of Sakuya will appear. Keep repeating the process for a new statue every time.