Descend
Inside the building is the Winter Cow. You need to see it, so you go inside. It is deep down in there, and you'll have to descend to reach it.
Focus on descending the stairs. There are many signs that say "To Winter Cow: descend" with an arrow pointing down. "I guess I'll have to descend," you say.
こう
お, ふ
None
You descend to the bottom and there it is, the Winter Cow. You walk up to the cow, and it swings its head back to see you. Instead of a cow's face, it's こういち's face.
"Hello, thank you for descending all the way down here to see me," says the Winter Cow with こういち's face. "You thought you could use the Winter Cow to stop me, but as you can see, I got here first."