Struggle in the Secret Hot Spring

Riku recieves a letter from Teru. It says that he needs his help at the Kitaguni Hot Spring Village Shinzansou. It turns out that Teru ate a lot of food that wasn't his at an inn in Shinzansou. So, to pay off his debt, he's working for the inn. But the real reason why Teru requests Riku's aid is that he needs his help in getting rid of the demons that have been attacking the people of the inn.