The Book of Grandchildren ( Natsume Yuujinchou X Nurarihyon no Mago)

While on their way back to the house, Natsume and the self-proclaimed bodyguard, Nyanko-sensei meet a youkai who want to express his gratitude to Natsume for his kindness on returning his name. But instead of helping Natsume, the youkai transport him and Nyanko-sensei to another city to help them searching for youkai...