S1·E19 String from the Sky

Seijirou is fascinated by the stars and enjoys stargazing. One day he was by the riverbed with the village nanny Fuki when she notices a string coming down the sky and as she tries to pull all of a sudden she disappears, right before Seijirou's eye. Ginko is travelling through the mountains and is being followed by a peculiar girl. It turns out that it's Fuki, who has been exposed to a strong Mushi presence and can't be seen by anyone.