Soak the chestnuts at least eight hours but preferably over night for a sweeter flavor. Don't throw away the soaking water.
Organic chestnuts are preferable.
Using a big enough bowl to allow for expansion by up to a factor of five, soak the hijiki for at least an hour. Longer makes no difference. Retain the soaking water, but leave out any sandy stuff that accumulates at the bottom of the bowl. Mix the brown rice and sweet rice, and wash and drain them a few times until the water clears. Put it in a pressure cooker with the rice.