Natsume Takashi can see and have communication with what other people cannot see. Madara had contract to get Yujin-cho after Takashi dies. In Hyakki-Yako-sho, Aoarashi had contract with Kagyu to help Ritsu until he dies. That's fine, I like story like this, not only stories of cute girls.
One thing, Grandma of Takashi is wearing uniform which was commonly seen in 70s, 80s. So, she had a child