S1E10 : The White Which Lives Within the Ink Stone

Some kids enter Adashino-sensei's shed and find a lot of strange things, but there's one thing in particular that interests them. It's night and Adashino-sensei is called upon to look at one of the kids, a girl who has become bitterly cold, and the cause is a mysterious ink stone she touched. Luckily for Adashino-sensei, Ginko is passing through the village, and he shows him the ink stone, which he identifies it as a "Kumohami".