Tanuma's father leaves on a trip, yet a strange youkai invades his house, spreading miasma that make all the nearby youkai suffer. Natsume tracks down the youkai, and it is revealed he was once a resident in a youkai village. A portal opened for a short time during a human ceremony, where he took his sister to watch. However, they became trapped in the human world, and his sister died. After returning to the old temple where the ceremonies were held, the portal opens and he returns home.