Sakura namiki no kare

From the day that a picture of a row of cherry trees in a desolate winter was obtained, every time Natsume wakes up, his rooms is covered in petals. Trying to solve the root of this activity, Natsume and Nyako Sensei try and return the picture to Miya, a shadowy figure who accompanies the picture. But why can't they return it to Miya...?