Susano will, uh, run off again to avoid having to break the boulder. Head
back to his house to find him sleeping at his training ground behind it. If
you talk to him he'll mutter that he's all out of sake. Hmm, perhaps if we
get him more? If you talked to Kushi you'd know that she's the one that
brews the sake.

Kushi can't make sake while her mill's water wheel is broken, though.
Scribble all over it to Rejuvenate the broken bit, then head inside the
mill. Talk to Kushi and she'll thank you for fixing the mill, and as a
reward will drop the Vista of the Gods sake. Bite it to pick it up, then
leave and head back to Susano.

After approaching him, he'll be ready to start training. Finally! Talk to
him to get him to train by slicing straw dummies. Susano isn't exactly a
competent swordsman, so when he slices the dummies (and the rock at the
end), you'll need to Power Slash them to destroy them instead. Well,
whatever builds self-esteem I guess. Repeat this process for the boulder
blocking Kamiki's exit.

Talk to Kushi (that woman in the rice fields) and she will tell you to go talk
to Susano. Head over to that big hut across the river from Kushi's house and
head to the basement where you will see Susano sleeping like a rock. You can't
wake him up now so go outside of the hut and head up the path to the huge
boulder that is blocking the way to the Shinshu Field. Talk to the Merchant
who is trying to move the boulder and a battle will start between you and a
few monsters that appear out of nowhere. Once he talks to you about getting
Susano, go get Susano by going back to his hut and tackleing him with the
Square button to wake him up.